you must have something (eg, av cleaner) causing the problem. but you can save your preferences to easily restore (assuming you've already tried sync and that fails).
In addition to resetting preferences as suggested by Keith, I would also like to inform you this also happens when we are working on network profile.
If it does not work after resetting preferences please reply with following details
Operating System(Exact version of Windows or MAC)
Exact version of InDesign
What type of user account your are using (Local Admin or Network profiles)