I had this issue before, I'm trying to remember what I did to resolve the issue. Have you tried from an outside source, not just inside the network? Sometimes the machine might have security set too high, that fixed it once but not the first time. Possible a path reference?
Just tossing out ideas that might hold you over until I can remember the answer or until support replies.
I'll try and remember and get back to you.
SQL 2008, Visual Studio 2010
Source: C#
Version: AspDotNetStorefront ML 8.0.1.1/8.0.1.1
Framework: .Net 4.0 (Running)