A Serious Error Has Occurred

Problem

when loading a save game I get the following error message:  A serious error has occurred while loading <name of the savegame>.sims3. It is strongly recommended that you restart the application.

Cause

The game is not able to read some files because they are locked/read-only by another application or folder.

Solution

See this posts for further infos and a solution

Also make sure that your Antivirus program is not scanning your hard drive while you play