A user action compiled for v6 will not work with v7 (but you should get a class or interface error when building, not an error when opening the project). I was also able to open the v6 User Actions.bld sample in v7, save and reopen, and build (it did fail at the .NET Step step, as expected). You would need to recompile the user action after updating the COM reference to VBP7 to call from v7.
http://www.kinook.com/VisBuildPro/Ma...albuild6_x.htm
What exactly do you mean by "the dll that is causeing the error is the same one I attach to in the VS project"? How do you know what DLL is causing an error?