XP_CMDSHELL

I am attempting to give access to the xp_cmdshell to two windows groups on my server.

What I have set up is this:

In The master database, I have given my user ( which is actually a group...DOMAIN\GroupName ) Execute permission on the xp_cmdshell object.

I have enabled the actual xp_cmdshell feature via the script:

-- To allow advanced options to be changed.
EXEC sp_configure 'show advanced options', 1
GO
-- To update the currently configured value for advanced options.
RECONFIGURE
GO
-- To enable the feature.
EXEC sp_configure 'xp_cmdshell', 1
GO
-- To update the currently configured value for this feature.
RECONFIGURE
GO

When I attempt to access the xp_cmdshell via my application, I recieve the following error:

System.Data.SQLCLient.SQLEXception The xp_cmdshell proxy account information cannot be reteieved or is invalid

The other item of not here is that this only occurs on windows 7.  When i install this app on XP all flavors, I never run into this, and have not had to create a proxy account, and i do not even know what that refers to.

Could anyone point me in the right direction?

Thanks,

Doug