OMW. Helped out another programmer at one of the sister companies of the company where I work via email today. First, the required COM DLLs weren't present, then I tried to get them for her from other projects that we did that used the same libraries, then she was getting “Exception of type 'System.Windows.Forms.AxHost+InvalidActiveXStateException' was thrown.” 24 emails later, it seemed like it would never end!
Eventually got an installer for her for the Kodak Image Library that was residing in a rather dusty directory on one of our servers (that thing is like flipping hen's teeth on the Internet!). That seemed to work, but then the same exception popped back up.
Guess what now? We forgot that the now-correctly-installed-and-registered ActiveX control wasn't on the form because, well, it wasn't correctly installed and registered. I supposed I should mention that she reinstalled her laptop two days ago and she also told me that she was modifying copied code. She put the control on the form and finally, Finally, FINALLY the thing worked.
1) If you format and/or reinstall your developer machine, make sure that the required libraries and project dependencies are installed.
2) If you are installing the said libraries and project dependencies during development, drop the control back onto the form!
She's very junior and is learning C# while she is coding this app, so this was plain inexperience on her part and ASSumption on my part.
Bleugh. But at least it's solved! :-)