If you’re developping .NET add-ins for 3rd party software, and want to move on to Visual Studio 2010, then this tip will certainly save you a lot of frustration.

Under VS2008, it was possible to place breakpoints in the add-in code, and when launching the host application from VS.NET’s debugger, those breakpoints would be hit as expected.

Under VS2010, the game changes. By default the debugger attached is the one for version 4.0 of the framework. If the host application targets the .NET 2.0 runtime, then the debugger just doesn’t see the breakpoints and sails right past them.

The workaround is easy enough. Just modify (or create one if it doesn’t exists) the HostApp.exe.config file to include the following:

<startup useLegacyV2RuntimeActivationPolicy=”true”>
  <supportedRuntime version=”v2.0.50727″/>
</startup> 

For more details:

An MSDN forum post
A Microsoft Connect entry