Why 503 exception met?

When I create community, role and asset type by web service api in sequence, I got this exception,

AxisFault
faultCode: {http://xml.apache.org/axis/}HTTP
faultSubcode:
faultString: (503)Service Unavailable
faultActor:
faultNode:
faultDetail:
{}:return code: 503
Error 503: The maximum number of sessions for this account has been reached. Log out from existing sessions or ask the system administrator to increase the maximum number of sessions per user.

{http://xml.apache.org/axis/}HttpErrorCode:503

(503)Service Unavailable
at org.apache.axis.transport.http.HTTPSender.readFromSocket(HTTPSender.java:744)
at org.apache.axis.transport.http.HTTPSender.invoke(HTTPSender.java:144)
at com.ibm.ram.internal.client.RAMHTTPSender.invoke(RAMHTTPSender.java:41)
at org.apache.axis.strategies.InvocationStrategy.visit(InvocationStrategy.java:32)
at org.apache.axis.SimpleChain.doVisiting(SimpleChain.java:118)
at org.apache.axis.SimpleChain.invoke(SimpleChain.java:83)
at org.apache.axis.client.AxisClient.invoke(AxisClient.java:165)
at org.apache.axis.client.Call.invokeEngine(Call.java:2784)
at org.apache.axis.client.Call.invoke(Call.java:2767)
at org.apache.axis.client.Call.invoke(Call.java:2443)
at org.apache.axis.client.Call.invoke(Call.java:2366)
at org.apache.axis.client.Call.invoke(Call.java:1812)
at com.ibm.ram.repository.web.ws.core.v72.RAM1SoapBindingStub.getAdminGroups(RAM1SoapBindingStub.java:8623)
at com.ibm.frwks.industrial.lcm.IndFrwksRAMConfigHelper.getCommunityByName(IndFrwksRAMConfigHelper.java:347)
at com.ibm.frwks.industrial.lcm.IndFrwksRAMConfigHelper.createCommunity(IndFrwksRAMConfigHelper.java:82)

And I check the active session in ram web console, then I got
Error 503: The maximum number of sessions for this account has been reached. Log out from existing sessions or ask the system administrator to increase the maximum number of sessions per user.

How can I do now? Anyone else met the same problem? And your idea? Thanks.