Hi, no worries, thanks for the reply. Regarding:
1) No, when I restored 10.4.1, I did not check to see if 1.3.1 GPT reappeared automatically before I re-installed it again deliberately.
2) Yes, after deliberately re-installing 1.3.1 GPT, it did appear in Add/Remove programs list. And yes, when I tried to upgrade to 10.5 again, I did first uninstall 1.3.1 GPT and the FMV add-in along with 10.4.1 and then upgraded to 10.5 and installed 1.3.2 FMV and GPT but the GPT gave red X's and did not work.
3) Yes, that's correct, and I don't think any errors or warnings were reported.
4) I would like to upgrade to 10.5 / FMV 1.3.2 if possible, but I needed to use the Video Multiplexer GP tool so I downgraded to 10.4.1/ FMV 1.3.2, which works, but it looks like I have to manually re-add the GP tools toolbox to each ArcMap session.
Thanks