error when connecting to SQL Server - Login failed for user '(null)'

[Don]

When I attempt to access a SQL Server database from my ASP.NET 1.1
application I get the folllowing error:
Login failed for user '(null)'. Reason: Not associated with a trusted
SQL Server connection.

I have impersonate set to true with the following setting in my
web.config file.
<identity impersonate="true" userName="" password=""/>

This project had been working fine. A few weeks ago I installed Visual
Studio 2005 and I've been working in it. When I went back to VS 2003
to work on this application I had the error above. I have verified
that IIS is using ASP.NET version 1.1.4322 for this application.

This application is used by at least 4 other people and is stored in
Source Safe. We all got the latest version and only I am having the
problem. This indicates that my web.config setting are correct.

I've compared my IIS settings with those of 2 other developers and
didn't notice any differences.

I've used SQL profiler to see what is happening in SQL Server and all i
see is 'Audit Login Failed' and the error message above. There is no
entry for NTUserName or Login Name. When other developers login SQL
Profiler shows the NT UserName as ANONYMOUS LOGIN and the LoginName as
NT AUTHORITY\ANONYMOUS LOGIN.