> The control was designed in this project, it has been closed an re-opened.

That could be the problem. Try moving the control to *another* project. Compile this *other* project as a DLL and then reference this *other* project in the one that you want to drop the control in.

.NET does not have the concept of "VCX" files. Therefore it is a little bit of a pain to have to create a separate DLL, compile it, and then reference it to get it to recognize the new control.