You never know. Its just a good maintenance practice especially after adding or deleting software from your Mac.Usually deleting prefs and the cache will fix things.
Your really need to find the Preview Files folder and delete the preview files as well. More important than the Permissions.
Tom Daigon
Avid DS / PrP / After Effects Editor
http://www.hdshotsandcuts.com
Mac Pro 3,1
8 core
10.6.8
Nvidia Quadro 4000
24 gigs ram
Maxx Digital / Areca 8tb. raid
Kona 3