This could be an issue with your folder permissions. I would double check that you have read & write privileges to the following folders:
Macintosh HD : Users : (User name you log in with) : Library:Application Support : Graphisoft : ArchiCAD AutoSave Folder as well as the TW data folder if this is happening in teamwork.
Another cause could be virus protection. If you are using any type of virus protection you could try turning it off and seeing if the issue persists.
Lastly do you know if you are using Network home in your office?