Hi. I have a two PC network where QB behaves odd. PC 1 is Windows 10 and the data file is stored there. PC 2 is Windows 7. Running QB Premier 2014. I know it is officially not supported by Win10, but blah blah blah. If that really is the issue, I'll take your word for it but I am surprised. Anyway so: all necessary networking tweaks have been done as proved by the fact that multi-user DOES work. HOWEVER, and here's the weird bit, for networking access to work, PC 2 MUST login first. It breaks down thus:
Both PC's can access the data file in single-user mode.
If PC 2 logs into the file and turns on multi-user, then PC 1 is able to connect concurrently.
If PC 1 logs in and changes to multi-user, PC 2 gets the error that says "although we can see PC 1 should be able to share this file, you seem to have a firewall error which is preventing it".
For a final test I turned the firewall on PC1 off completely, and it didn't make any difference, so it doesn't seem likely to be a firewall error. In any case, as mentioned, as long as PC2 logs in first, we don't get that error anyway.
I have not seen that before, but I can tell you that 2015 was the first supposedly supported for win10 and it was iffy, 2020 is out and seems stable on win10, that is 5 years between what you have now and current.
There is a real possibility that your 2014 file will not update seamlessly, you may have to step it up using an in between year. make a back up, restore in a newer version, make a back up, restore in the new current version