I'd start with safe boot #3 below. Report the results.
You may want to run these "standard" fixes if the problem persists.
1) Check the amount of free space on your harddrive. You should have a several gigs free.
2) You should run disk utility
a) verify the disk
b) update your permissions.
3) Try a safe boot.
Shutdown your machine. Hold down the shift key. Poweron. Wait awhile Wait awhile while you harddrive
is being checked.
http://support.apple.com/kb/ht1455
4) You may want to run applejack to clean up your machine.
http://applejack.sourceforge.net/
a lot more ways to fix your Mac.
http://www.thexlab.com/faqs/faqs.html