Hi Purenergy,
When I got this "a serious error has occurred" message, my game was corrupted due to a crash while saving. I only got that error with that one save file, so there was no reason for a reinstall, as the problem was that save file, not the game itself. Did you try loading your other files yet? If you get that with all files, I guess you have to do a factory reset and if that does not help, a complete reinstall.
You will have to install your store content again after factory reset / reinstall. You can use your saved games again if you store them somewhere and then place them back to the 'Saves'-folder, unless they are corrupted which might be the case here.
In case you have not read these threads already: There are stickied threads on this Technical board about factory reset and re-install... Also if you have this problem with only one game file, see the sticky about back-up files.