It sounds like you may be experiencing problems relating the Win or Mac filecache depending on your os. This can sometimes happen when you install extensions. When installing you should be selecting 'yes to all' to overwrite any files.
If this is the problem deleting this file and restarting should get you going. Here is a link to a page that lists the steps to do this:
Please try deleting this cache file and letting us know how it works for you. Also, if you continue to have problems please post back with the specific errors you are getting and exactly when they occur for you.