Error in retrieving the mapped user??

I am using this code for retireval of the mapped user data:

IPortalRuntimeResources obj1 = PortalRuntime.getRuntimeResources();

IService obj2 = obj1.getService(IUserMappingService.KEY);

IUserMappingService iums = (IUserMappingService)obj2;

but I m not able to proceed beyond this line:

IUserMappingService iums = (IUserMappingService)obj2;

the system is not giving any exception bcoz the loggers in the catch block are not printed. but its not executing beyond this line.

I m using EP6.0 SP9.

I m trying this code in the RF framework(Repository Manager)

Kindly help.