Try setting up another admin user account to see if the same problem continues. If Back-to-My Mac is selected in System Preferences, the Guest account will not work. The intent is to see if it is specific to one account or a system wide problem. This account can be deleted later.
If the problem is still there, try booting into the Safe Mode. Shut down the computer and then power it back up. Immediately after hearing the startup chime, hold down the shift key and continue to hold it until the gray Apple icon and a progress bar appear. The boot up is significantly slower than normal. This will reset some caches, forces a directory check, and disables all startup and login items, among other things. If the system operates normally, there may be 3rd party applications which are causing a problem. Try deleting/disabling the third party applications after a restart. For each disable/delete, you will need to restart if you don't do them all at once.
I know this post is old, but I have discovered what causes the corruption of this plist. When I boot to my Windows partition in Bootcamp and then come back to OS X, the plist becomes corrupt and causes this issue. I had originally thought the problem may have been caused by Bootchamp which is a third party app used to easily and quickly boot to th Bootcamp partition. I deleted Bootchamp and still have the plist becoming corrupt when booting to Windows.