Can't log in

Greetings,
I just imported a backup that I exported recently.
After a 17 hour import, I can see all accounts and can see the total mail from each account is accurate.
However, I can't log in to any account except admin. Even after a successful password change, I still can't log in.
The export came from A SLES server using ZCS 8.6 and the import went to an Ubuntu bionic server running ZCS 8.8.15.

Is there some step I'm missing to be able to log in to the imported mail accounts?

Thanks in advance
iomari