There are a lot of things that can go wrong on any kind of database upgrade. Hopefully the other site backed up all of it's data before they installed the upgrade.

Sometimes during an upgrade, if they haven't installed all of the patches before upgrading, it can go terribly wrong. If things were not done in a certain progression, it can go wrong.

They should be able to re-install their previous database and platform from a back up and all should be there, providing the back up was done properly with no errors.

How frustrating it can be to upgrade and have it go kaflooey. I hope all gets worked out asap.