Error when using Powershell in FIM workflow

Hi,

I am using a PowerShell script to fetch the groups for a user. The script works perfectly fine in Powershell Console. The moment I use it in FIM Workflow, I get the following error.

Error= The web service client has encountered the following class of error: IdentityIsNotFound
Details: Additional Text Details: The requestor's identity was not found.
Correlation Identifier: 705c19b5-0d03-45c0-b306-c46553eb804e
Failure Message:
Request Identifier:

I tried changing the filter in all possible ways and still landup getting the same error. Can someone help me here?

Thanks in Advance

Veena