I've tried to find this in Knowledge Base without luck.
Backed up database before upgrade, so i guess that I can recover by tomorrow morning... but I really want the new sync!
Installed 3.5.1 without any problems.
Login to database just keeps the spinning symbol while saying "Loading Data"...
What have I done wrong and how should I recover... hopefully useing 3.5.1

It's possible your db is not frozen. It can take quite a while to update when the first time you open it in 3.5. Try to leave it and see if it eventually starts up.

Thank you, Howard. Unfortunately the "Force Quit" box shows that Daylite is "not responding"