interopforms

VB 6 InteropForms: The file [...] was not registerable as an ActiveX Component

I am working my way through the walk-through and I got as far as trying to load the control into the VB 6 toolbox. I can load the DLL as a reference, but not as an ActiveX Component. When I try I get the message "InteropForms: The file [...] was not registerable as an ActiveX Component.". I can create the control at runtime as a normal...