Jojojo, I got the same message that I had to reinstall the base game. Doing a factory reset didn't work. So yes, I did uninstall and reinstall everything (and since I have all the EPs and most of the SPs, it took a while).
The game will install a very large patch that will take you up to 1.55 right after you reinstall the base game, and you'll get a few small patches as you go.
Everything you have that is registered on Origin can be downloaded from Origin, so you don't have to look for your discs.
I've had no problem with new games, and both my Immortal and Decadynasty saved files are working well. I did have some trouble with one saved file, but just removed the family and started them over in a new game.
A complete uninstall and reinstall (in order) takes some time -- 45 minutes to an hour for EPs, about 20 minutes for SPs, but it is worth the effort.