Crispin -

That's more confusing now.  If I just connect to SQL server (say, with Management Studio) using Windows Authentication (or, even, SQL Authentication) and run my stored procedure, I can...

oh, and i'm running Vista, if it makes a difference.

edit: the issue is also present when running under WinXP, so OS doesn't appear to make a difference.

I'll also throw this...

I'm having the same problem.

My calls to xp_regread work fine when I'm connected as myself, but my application is using an application role to provide access to all...