Spurious “cannot load control, license not found” error?

Question

When I try to load a form in the designer, it shows \"runtime error 0\" and produces a log file which contains:

Line 15: Cannot load control xxxx; license not fo         


        

Answer 1

(Answering my own question, should anyone else run into this again).

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As far as I can determine this error was caused by either a subtly corrupt FRX file and/or an FRM/FRX file pair being out of sync.

By going back in source control I could eventually locate a revision where there was no problem. This alone seemed to eliminate anything in the computing environment from being the cause. (ie, bad VB6 installation, disk space, etc. etc.)

I manually re-did certain changes and brought that older code back up to date, and so far the problem has not reappeared.

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EDIT the struck-out text was not incorrect but was not specific enough -- I have since learned what seems to be the root cause.

The problem was that we loaded a 32-bit ICO file (icon) into an imagelist in one of the VB6 forms. Now, traditionally 32-bit color icons were not usable in VB6 and you would get an error even trying to do this. However for some reason certain Windows PCs will now allow this - which can be a time bomb.

The problem is: forms saved that way can cause the errors in this question when run on a different PC which does NOT support such icons.

This will occur in the IDE when the form is loaded, OR if a compiled EXE is run on a different computer which respects the original VB6 icon limitations!

I don't know why the totally meaningless "licensing" error message is shown when this happens.

In my case we didn't intentionally introduce this icon, it was a mistake, and so it took a LONG time to debug and eventually figure this out (plus some very valuable advice from people on VBForums).

I've created a different question specifically to try and get at what underlying element of Windows has changed causing this problem.