File association won't change to the proper program

Hi All,
I have an file association issue that I haven't been able to solve.
I've been using a CAD tool GC-Prevue (from GraphiCode - Software Innovations for Electronics Manufacturing - Index) with a *.gwk extension. Recently it started associating to Acrobat X Pro. When I right-click "Open with" Acrobat is the only program listed. I tried Browse to the GC-Prevue *.exe file, choosing it and trying to open but nothing changes. It doesn't open and the "Open With" window remains with only Acrobat as the choice.
I uninstalled and reinstalled Acrobat. No Luck.
I uninstalled and reinstalled GC-Prevue. No Luck.
FWIW: I can always open the program and browse to the file I need to open and there's no problem.
Suggestions anyone?
Thanks in advance for your replies/advice.
Best,
/jdU

Have you tried to change the file association in Control Panel > Default Programs (small icon view)?

Hi BJB, Thanks ... I gave that a try, but everything worked the same way with no correct results.
Very strange.
Might anyone else have a suggestion?
Thanks in advance for your consideration.
Best,
/jdU

If it's not malware then some system files aren't doing their job. Try running sfc /scannow from an elevated command prompt. This is the system file checker and it may ask for your Windows disk. If it does it has to be a Windows installation disk as an OEM recovery disk won't do. Try it anyway.

Ask if you need any help with running an elevated command prompt.

Thanks Callender. It sounds like you have the answer I need, but I'm feeling pretty stupid:
I can see this:
FileTypesMan v1.68 - File Types Manager for Windows
Copyright (c) 2008 - 2014 Nir Sofer
But I can't locate the download link.
Would you point me in the right direction.
Appreciate!
/jdU

OMG ... D'oh!
How many times have I told folks "Scroll down."?
LOL
Thanks so much!
/jdU