"So, I simply re-transferred the proseries client file from 2021 into 2022 and then imported the trial balance again...So...that worked for me....So, I am still using ATBWU."

So your workaround appears to be to re-transfer the prior year's file into 2022, again, and see it re-established the link.

Sounds like some sort of program or file corruption which Intuit ProSeries refuses to fix, considering it's just a file linkage issue as it has No other practical purposes like number calculation.

Guess Intuit has finally decided NOT to support the file link anymore!

It was one of the top reasons to continue with ProSeries as some of us still use ATB for Windows!

Concentrating on individual files now but will use your suggestion later.

Thanks!