Meet Random Error when open report document when using SAP web intelligence

Dear All,

Anyone has some idea about the following error?

When using the Web intelligence to open the report document, we randomly meet below error. And if we wait 1-2 hours. We tried to open the report again, then there will be no error.

Error: Open Document

While trying to invoke the method com.businessobjects.sdk.core.server.IServer.getServerContext()of xxx: object returened from com.businessobjects.rebean.wi.impl.servcies.DocumentInstancesManagementServicesImpl.getServer(com.businessobjects.sdk.core.context.IContext.com.businessobjects.rebean.wi.model.engine.IDcumentInstance)(Error:INF).

BO version,

SAP BusinessObjects BI platform4.1 SP5 which upgrade from 4.1SP01.