From MacFixIt.com wrote:
General tip: Checking your user Library folder Many individual application issues that occur during a major Mac OS X upgrade can be solved via a process similar to the method used for troubleshooting Extension conflicts under Mac OS 7, 8 and 9. It's a shotgun technique, but one that has proved fruitful in many cases.
The process is as follows:
Move your User library folder (~/Library) to a different location, such as the Desktop.
Log out of your account, then log back in. A new user library folder without any customization you may have performed will be created.
Perform the task that was previously causing issues (e.g. launching an application, etc.), which should now work as expected.
Move a few folders from the old user Library folder (on your Desktop, or wherever you placed it) back into the new Library folder.
Again, log out and back in.
Perform the task that was previously causing issues and check for persistence of the issue.
Repeat steps 4-6 until the problem returns. At this point you will have narrowed down the potential culprits. When a batch of folders causes the problem to return, examine the just re-added folders for user added elements that could be causing the issue, and eliminate them.