Error of using getEP5User

I used the following common methods to create resource context:

IWDClientUser wdClientUser = WDClientUser.getCurrentUser();

com.sap.security.api.IUser sapUser = wdClientUser.getSAPUser();

com.sapportals.portal.security.usermanagement.IUser ep5User = WPUMFactory.getUserFactory().getEP5User(sapUser);

IResourceContext resourceContext = new ResourceContext(ep5User);

I did not get any compilation error, however got runtime error at the method of creating ep5User....did not get specific error message, only got the following "

tacktrace: [Ljava.lang.StackTraceElement;@10f310f3"

The version of NWDS I used is 7.0 SP11P, and the portal version is EP7 SP9.

Thank you for any suggestions!

Rong