WAS shutting down abruptly while using BIRT API's

raravind

Dear All,
We are using BIRT 2.3.1 in our Application which runs on Websphere 6.1.0.21.
We have our Report Generator and our Report Viewer which call the BIRT Apis to generate the report.
We are calling the report generation through the stateless session bean from our Application.
Our OS is Windows 2003 and JVM supported by Websphere is JVM 1.5.
When we are subjecting this to performance testing and are repeatedly getting the error

"java.lang.OutOfMemoryError
at org.eclipse.birt.core.util.IOUtil.readUTF(IOUtil.java:1018)
at org.eclipse.birt.core.util.IOUtil.readString(IOUtil.java:689) ".

This error is repeatedly generated for us at periodic intervals and finally the websphere server is getting stopped.
Could you please suggest what is the reason for the same and help us?