How are you making this call? You'll only be able to lookup a Seam context after Seam has initialized and while you're within some web request.
So calling this method via a startup servlet will probably fail. Calling this method via an EJB or MDB that is executed via a non-web request (ie executed directly via IIOP) will also probably fail.
With few exceptions Seam only really works (has context) within the JSF lifecycle. It sounds like you may be trying to use it outside of this. Or you may simply have Seam misconfigured. I need more info please.
Thank Cptnkirk. it works now when i call session bean through JSF. i made a mistake that i call such session bean in a servlet.