We need to know the exact error. Please try again.
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
Macintosh-HD -> Applications -> Utilities -> 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.