RDM: "Unable to load diagram"

Hello,
I am using RDM on Tomcat on Windows.
When loading a simple diagram, I am getting the "Unable to load diagram" at the middle of the diagram area.
Sometimes I can display a very simple diagram. But most often I get this problem.
Note that I checked that Model import completed without problems.

I went to DM logs just after the message. The last error in the log is the following:

2013-09-02 11:14:13,293 [        http-bio-9443-exec-344] [] ERROR com.ibm.xtools.rmpx.common.exceptions.RmpxRuntimeException  - <rdf:RDF
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:err="http://jazz.net/xmlns/prod/jazz/foundation/1.0/">
  <rdf:Description>
    <err:detailedMessage rdf:datatype="http://www.w3.org/2001/XMLSchema#string"
    >
User: Lionel Mommeja
Rmps Request Line:
  GET https://9.100.81.175:9443/dm/diagrams/image?diagramUri=https%3A%2F%2F9.100.81.175%3A9443%2Fdm%2Fmodels%2F108&amp;tiled=true&amp;rmps.context=https%3A%2F%2F9.100.81.175%3A9443%2Fdm%2Fstreams%2F8&amp;dojo.preventCache=1378134860315 HTTP/1.1
Rmps Request Headers:
  host: 9.100.81.175:9443
  user-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:23.0) Gecko/20100101 Firefox/23.0
  accept: application/json
  accept-language: fr,fr-fr;q=0.8,en-us;q=0.5,en;q=0.3
  accept-encoding: gzip, deflate
  x-ibm-rmps-internal: true
  x-jazz-downstream-auth-client-level: 4.0
  content-type: application/x-www-form-urlencoded
  x-requested-with: XMLHttpRequest
  referer: https://9.100.81.175:9443/dm/web/projects/EBird%20-%20Smarter%20Fleet%20Models?rmps.context=https%3A%2F%2F9.100.81.175%3A9443%2Fdm%2Fstreams%2F8
  cookie: JSESSIONID=FD3A143E174D6A8C1D6E180F1110229A; net-jazz-ajax-cookie-rememberUserId=; jfs-oauth-realm-mapping=https%3A%2F%2F9.100.81.175%3A9443%2Fjts%3D0; jfs-oauth-access-token0=9a6ce40afd264d10b933ee6dab93a0f1; jfs-oauth-access_token-secret0=fV4Y2nC3c4Jqz2u7ih7FxTOUY4dcBP6OqcAAgZnRpHY; JAZZ_AUTH_TOKEN=9a6ce40afd264d10b933ee6dab93a0f1&amp;fV4Y2nC3c4Jqz2u7ih7FxTOUY4dcBP6OqcAAgZnRpHY; JSESSIONIDSSO=D4209A879AB9737D38EA8D82C0C06B6B
  connection: keep-alive
  X-ibm-internal-dm-request-correlation-ID: 0870b8d5-9cc6-404d-b9b3-4edc5e96e56c
Jfs Request Line:
  GET https://9.100.81.175:9443/rsadm/com.ibm.xtools.rmps.frontservice.contentprovider.IDiagramServiceProvider/http%253A%252F%252Frmps.xtools.ibm.com%252Fnorvo/getTileDescriptor?tiled=true&amp;dojo.preventCache=1378134860315&amp;diagramUri=https://9.100.81.175:9443/dm/models/108&amp;rmps.context=https://9.100.81.175:9443/dm/streams/8 HTTP/1.1
Jfs Request Headers:
  Accept: */*
  Referer: https://9.100.81.175:9443/dm
Jfs Response Headers:
  Server: Apache-Coyote/1.1
  Content-Type: text/html;charset=utf-8
  Content-Length: 2972
  Date: Mon, 02 Sep 2013 15:14:12 GMT
  Connection: close
  X-ibm-internal-dm-request-correlation-ID: e53ac42f-8746-450e-9885-dcabe05500e2
Jfs Response Body:
  &lt;html&gt;&lt;head&gt;&lt;title&gt;Apache Tomcat/7.0.32 - Error report&lt;/title&gt;&lt;style&gt;&lt;!--H1 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:22px;} H2 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:16px;} H3 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:14px;} BODY {font-family:Tahoma,Arial,sans-serif;color:black;background-color:white;} B {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;} P {font-family:Tahoma,Arial,sans-serif;background:white;color:black;font-size:12px;}A {color : black;}A.name {color : black;}HR {color : #525D76;}--&gt;&lt;/style&gt; &lt;/head&gt;&lt;body&gt;&lt;h1&gt;HTTP Status 500 - java.lang.NullPointerException&lt;/h1&gt;&lt;HR size="1" noshade="noshade"&gt;&lt;p&gt;&lt;b&gt;type&lt;/b&gt; Exception report&lt;/p&gt;&lt;p&gt;&lt;b&gt;message&lt;/b&gt; &lt;u&gt;java.lang.NullPointerException&lt;/u&gt;&lt;/p&gt;&lt;p&gt;&lt;b&gt;description&lt;/b&gt; &lt;u&gt;The server encountered an internal error that prevented it from fulfilling this request.&lt;/u&gt;&lt;/p&gt;&lt;p&gt;&lt;b&gt;exception&lt;/b&gt; &lt;pre&gt;javax.servlet.ServletException: java.lang.NullPointerException
    com.ibm.xtools.rmps.renderingapp.servlet.internal.AnnotationServlet.service(AnnotationServlet.java:291)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    org.eclipse.equinox.http.registry.internal.ServletManager$ServletWrapper.service(ServletManager.java:180)
    org.eclipse.equinox.http.servlet.internal.ServletRegistration.service(ServletRegistration.java:61)
    org.eclipse.equinox.http.servlet.internal.ProxyServlet.processAlias(ProxyServlet.java:126)
    org.eclipse.equinox.http.servlet.internal.ProxyServlet.service(ProxyServlet.java:76)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    org.eclipse.equinox.servletbridge.BridgeServlet.service(BridgeServlet.java:120)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
&lt;/pre&gt;&lt;/p&gt;&lt;p&gt;&lt;b&gt;root cause&lt;/b&gt; &lt;pre&gt;java.lang.NullPointerException
    com.ibm.xtools.rmps.renderingapp.extensionhandler.internal.JfsRenderingClient$1.getUserName(JfsRenderingClient.java:389)
    com.ibm.xtools.rmps.renderingapp.servlet.internal.AnnotationServlet.service(AnnotationServlet.java:286)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    org.eclipse.equinox.http.registry.internal.ServletManager$ServletWrapper.service(ServletManager.java:180)
    org.eclipse.equinox.http.servlet.internal.ServletRegistration.service(ServletRegistration.java:61)
    org.eclipse.equinox.http.servlet.internal.ProxyServlet.processAlias(ProxyServlet.java:126)
    org.eclipse.equinox.http.servlet.internal.ProxyServlet.service(ProxyServlet.java:76)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    org.eclipse.equinox.servletbridge.BridgeServlet.service(BridgeServlet.java:120)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
&lt;/pre&gt;&lt;/p&gt;&lt;p&gt;&lt;b&gt;note&lt;/b&gt; &lt;u&gt;The full stack trace of the root cause is available in the Apache Tomcat/7.0.32 logs.&lt;/u&gt;&lt;/p&gt;&lt;HR size="1" noshade="noshade"&gt;&lt;h3&gt;Apache Tomcat/7.0.32&lt;/h3&gt;&lt;/body&gt;&lt;/html&gt;
com.ibm.xtools.rmps.frontservice.jaf.jfsclient.RmpsRuntimeException: 500 (CRITICAL) :Internal Server Error&#xD;
    at com.ibm.xtools.rmps.frontservice.jaf.jfsclient.JfsSystemClient.execute(JfsSystemClient.java:575)&#xD;
    at com.ibm.xtools.rmps.frontservice.jaf.jfsclient.JfsSystemClient.execute(JfsSystemClient.java:405)&#xD;
    at com.ibm.xtools.rmps.renderingapp.contentproviders.RenderingAppClient.execute(RenderingAppClient.java:179)&#xD;
    at com.ibm.xtools.rmps.renderingapp.contentproviders.RenderingAppClient.getRequest(RenderingAppClient.java:48)&#xD;
    at com.ibm.xtools.rmps.renderingapp.contentproviders.RenderingAppClient.getRequest(RenderingAppClient.java:57)&#xD;
    at com.ibm.xtools.rmps.renderingapp.contentproviders.internal.RenderingAppDiagramServiceProvider.getTileDescriptor(RenderingAppDiagramServiceProvider.java:93)&#xD;
    at com.ibm.xtools.rmps.diagrams.internal.DiagramsFrontService.rmpsGet(DiagramsFrontService.java:208)&#xD;
    at com.ibm.xtools.rmps.frontservice.jaf.RmpsFrontService.rmpsService(RmpsFrontService.java:388)&#xD;
    at com.ibm.xtools.rmps.frontservice.jaf.RmpsFrontService.doGet(RmpsFrontService.java:542)&#xD;
    at com.ibm.team.jfs.app.servlet.AppContainerServlet.dispatchRequest(AppContainerServlet.java:170)&#xD;
    at com.ibm.team.jfs.app.servlet.AppContainerServlet.service(AppContainerServlet.java:281)&#xD;
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)&#xD;
    at com.ibm.team.repository.servlet.AbstractTeamServerServlet.service(AbstractTeamServerServlet.java:1695)&#xD;
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)&#xD;
    at org.eclipse.equinox.http.registry.internal.ServletManager$ServletWrapper.service(ServletManager.java:180)&#xD;
    at org.eclipse.equinox.http.servlet.internal.ServletRegistration.service(ServletRegistration.java:61)&#xD;
    at org.eclipse.equinox.http.servlet.internal.ProxyServlet.processAlias(ProxyServlet.java:126)&#xD;
    at org.eclipse.equinox.http.servlet.internal.ProxyServlet.service(ProxyServlet.java:76)&#xD;
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)&#xD;
    at org.eclipse.equinox.servletbridge.BridgeServlet.service(BridgeServlet.java:120)&#xD;
    at com.ibm.team.repository.server.servletbridge.JazzServlet.service(JazzServlet.java:68)&#xD;
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)&#xD;
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)&#xD;
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)&#xD;
    at com.ibm.team.repository.server.servletbridge.BridgeFilter.processDelegate(BridgeFilter.java:139)&#xD;
    at com.ibm.team.repository.server.servletbridge.BridgeFilter.doFilter(BridgeFilter.java:172)&#xD;
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)&#xD;
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)&#xD;
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)&#xD;
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)&#xD;
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)&#xD;
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)&#xD;
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)&#xD;
    at org.apache.catalina.authenticator.SingleSignOn.invoke(SingleSignOn.java:336)&#xD;
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)&#xD;
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)&#xD;
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1002)&#xD;
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:585)&#xD;
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)&#xD;
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:908)&#xD;
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:931)&#xD;
    at java.lang.Thread.run(Thread.java:738)&#xD;
</err:detailedMessage>
    <err:errorSeverity rdf:datatype="java:com.ibm.xtools.rmpx.common.exceptions.ErrorReport$Severity"
    >CRITICAL</err:errorSeverity>
    <err:errorMessage rdf:datatype="http://www.w3.org/2001/XMLSchema#string"
    >Internal Server Error</err:errorMessage>
    <err:errorStatus rdf:datatype="http://www.w3.org/2001/XMLSchema#long"
    >400</err:errorStatus>
  </rdf:Description>
</rdf:RDF>