Hi
There were two situations when you might run into this problem. First of them was that you're runnign a non-English Windows, where PCM 3 isn't supported. The second option is that you're running an English OS but a non-English localization, where PCM 3 is supported.
The current installer contains fix for 108020. This will allow a successful migration when OS is English but localization is non-English. This will not allow a successful migration when OS itself is non-English. There's no way to fix that, the problem is that registry keys in English and non-English OS aren't the same.
For you people who already have run into this problem and see the "Data Migration failed" -error there is an unsupported option which may allow a successful migration:
Note down the original PCM version and Autoupdate level.
Backup the database using the Backup facility.
Install the same PCM version on a clean Windows on a supported environment.
Uninstall PCM 3 on the original server to get Uninstall IDs required for license transfer.
Go to My Networking portal and transfer the licenses to the new Install ID.
Apply the licenses to the new server.
Update to the same Autoupdate level with the original server.
Restore the database to the new server with the Restore facility.
Upgrade the new server to PCM 4.
I have to stress again: this is an untested, unsupported recovery method, so if it fails there's nothing support can do for you. Before doing it you should restore the system from previous backup before the migration.
If it fails, there's only the other option left... doing a clean PCM v4 installation, and transferring the PCM v4 licenses to the new Install ID.