OK, here is some clarity on this issue:
1. We are using DNN 4.4.1, and the latest release of the Events module, circa March 2006.
2. We are using Visual Studio 2005.
3. When we open the EVENTS.SLN file, Visual Studio tells us that this file was created in an OLDER version of Visual Studio, and that it needs to be converted.
4. We choose to convert the file, since Visual Studio 2005 will refuse to open the file without conversion.
5. We "Start the website without debugging." Visual Studio rebuilds the project, and throws the errors listed in the first post of this thread.
I am guessing that the DNN core framework is a Visual Studio 2005 project (since the DotNet framework 2.0 was not supported in Visual Studio 2003), but the Events module was developed in Visual Studio 2003 (supported in DotNet 2.0 via backward compatibility).
Do we really need two versions of Visual Studio on our development machines to make this work, or can we do a proper conversion on the Events module and stay in Visual Studio 2005 for all of our development work? (I prefer the latter approach, for several reasons)