Issue Attaching to Exe to reverse Engineer

[TomB]

I am trying to reverse engineer a sequence diagram.
This is a C#, .NET 2.0 Application
I have imported all of our custom source code.
Our code runs as "plug-ins" in a 3rd party .NET application.
All of our code is a debug build and I have pdb files.
The 3rd party app is a release build w/o pdb files.
I have set my breakpoint in our custom code.
When I try and attach to the exe I get the message "No debug information available in target"
How can I get around this issue to rev-eng our custom code?

[TomB]

As a followup,
I can attach to this application in VS2K5, set a breakpoint at the same line of code and successfully debug.