Script receives 'Failed to acquire locks on requested sandboxes in 60000ms.'

I'm running a script that manipulates a sandbox by loading changesets programmatically; 2 out of 5 runs fails, arbitrarily it seems to me, with the error noted above.  The config is unique to the script and nothing else is accessing the sandbox - what is going on ?

2013-01-28 12:55:47,747 0: daemons for this config:
Port  Description
11869 Jazz CLI (3.1.0.v20120519_2357)
  /workspace/teymoub/rtc_wa/migration/test/upcore-4.1
 
2013-01-28 12:55:52,595 verify.py error: Exception raised rtc.py error: failed to execute RTC CLI command "lscm --non-interactive workspace replace-components -r 'pid11621' --all --baseline 'UPcore-4.1.14_20100824' --overwrite-uncommitted 'upcore-4.1 test WS' workspace 'upcore-4.1 test WS'":
com.ibm.team.repository.common.TeamRepositoryException: Failed to acquire locks on requested sandboxes in 60000ms.
    at com.ibm.team.filesystem.rcp.core.internal.rest.FilesystemRestClient.postRegisterSandboxes(FilesystemRestClient.java:1898)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:48)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:600)
    at com.ibm.team.filesystem.client.daemon.JSONHandler.handle(JSONHandler.java:322)
    at com.ibm.team.filesystem.client.internal.http.HttpConnection.readNextRequest(HttpConnection.java:628)
    at com.ibm.team.filesystem.client.internal.http.HttpConnection$1.run(HttpConnection.java:470)
    at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)
    at com.ibm.team.repository.common.internal.marshal.util.MarshallerUtil.decodeExceptions(MarshallerUtil.java:326)
    at com.ibm.team.repository.common.serialize.internal.JSONDeserializer.deserializeErrorObj(JSONDeserializer.java:955)
    at com.ibm.team.filesystem.client.internal.marshalling.ExceptionHandlingJSONDeserializer.deserializeErrorObj(ExceptionHandlingJSONDeserializer.java:128)
    at com.ibm.team.repository.common.serialize.internal.JSONDeserializer.deserializeException(JSONDeserializer.java:933)
    at com.ibm.team.filesystem.client.internal.marshalling.EObjectJSONDeserializer.deserializeError(EObjectJSONDeserializer.java:71)
    at com.ibm.team.filesystem.client.restproxy.RestInvocationHandler.executeRequest(RestInvocationHandler.java:267)
    at com.ibm.team.filesystem.client.restproxy.RestInvocationHandler.executeAndReturnResult(RestInvocationHandler.java:221)
    at com.ibm.team.filesystem.client.restproxy.RestInvocationHandler.invokeInternal(RestInvocationHandler.java:368)
    at com.ibm.team.filesystem.client.restproxy.RestInvocationHandler.invoke(RestInvocationHandler.java:311)
    at $Proxy1.postRegisterSandboxes(Unknown Source)
    at com.ibm.team.filesystem.cli.core.util.SubcommandUtil.registerSandboxes(SubcommandUtil.java:872)
    at com.ibm.team.filesystem.cli.core.util.SubcommandUtil.registerSandboxes(SubcommandUtil.java:866)
    at com.ibm.team.filesystem.cli.core.util.SubcommandUtil.setupDaemon(SubcommandUtil.java:1129)
    at com.ibm.team.filesystem.cli.client.internal.workspace.ReplaceComponentsCmd.run(ReplaceComponentsCmd.java:100)
    at com.ibm.team.filesystem.cli.core.internal.SubcommandLauncher.run(SubcommandLauncher.java:673)
    at com.ibm.team.filesystem.cli.core.internal.SubcommandLauncher.doStart(SubcommandLauncher.java:402)
    at com.ibm.team.filesystem.cli.core.internal.SubcommandLauncher.run(SubcommandLauncher.java:179)
    at com.ibm.team.filesystem.cli.client.internal.daemon.CommandLineClient.handleRequest(CommandLineClient.java:125)
    at com.ibm.team.filesystem.client.internal.http.ProtocolSwitchingHttpHandler.handle(ProtocolSwitchingHttpHandler.java:46)
    at com.ibm.team.filesystem.client.internal.http.HttpConnection.readNextRequest(HttpConnection.java:628)
    at com.ibm.team.filesystem.client.internal.http.HttpConnection$1.run(HttpConnection.java:470)
    at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)
Problem running 'workspace replace-components':
Could not register sandboxes.