Cannot add dll as reference in C++/CLI project
===

I am working on a C++/CLI project that makes use of a number of COM dlls that are part of an API provided by a third party, that I do not have the source code for.  I am using a number of the dlls without a problem but I am unable to add one of them as a reference to the project.  Whenever I try I get the error:

    Could not add a reference to file [dll file name] because it is neither a .NET assembly or registered ActiveX control.

I have registered the dll and can see it when I look it up in regedit.  I can see the type library when I open it in oleview. I was wondering if anyone might know why this error would occur, or where I might look to discover more about the problem.