This is the Leopard forum but you appear to have Lion. You would get faster help on the correct forum.
Try a permissions repair.
If you cannot do this or if does not cure the problem try the following:
1 - Restart Lion, and before you hear the chime, hold down the Command and R keys.
2 - On the Menu Bar select Utilities and then Terminal.
3 - Type the following in the Terminal window.
4 - Hit Return.
5 - Password reset utility will open but don't reset password.
6 - Click the Mac’s hard drive icon at the top and select your account.
7- Click Reset in 'Reset Home Directory Permissions and ACLs' at the bottom of the window.
8 - This will take a few of minutes. When it’s done, exit the programs you opened and Restart the Mac.