If you have a solution in Visual Studio which consists of both web- and class library projects, then you might get an alert box with the following message:

"The following module was built either with optimizations enabled or without debug information:

....

To debug this module, change its project build configuration to Debug mode. To suppress this message, disable the 'Warn if no user code on launch' debugger option."

Do this to get rid of the alert:
1. Right click the project giving the alert, choose “Properties”.
2. Choose “Build” and then “Advanced…”
3. Set Debug info to “full”.

Now the alert should be gone.

For some reason Visual Studio 2008 started closing my web.config file whenever I pressed Ctrl+S to save. First I thought it might be a new VS2008 “feature” but no, it turns out to be a bug in the ADO.NET Entity Framework Designer. Solution: uninstall ADO.NET Entity Framework Tools Preview or wait for a fix.

Thanks to Rich Strahl for figuring this out.