Seems like the server key doesn't match what's in SDMCFG.INI. Did you create a new server object in the database? If so, it's going to get a new key which the client doesn't have and isn't prepared to negotiate with.
If I test the new version on a few machines and it works I should be easily be able to upgrade all the devices in my groups. with 300+ groups I'd either have to write a script or spend all day clicking, I don't think I should have to write a script just to do a routine upgrade.
ideally I should be able to search for machines in all groups, select as many or as few as I want then edit the properties for the selection so I can easily change their file groups