You need to fix your disk permissions.
To fix your disk permissions, open the Disk Utility program found in the Applications > Utility folder on your hard drive root level directory. At the top of the Disk Utility window is a row of tabs. Click on the First Aid tab. On the left is a list of the disk and volumes mounted on your computer system.
You will need to click on your boot volume to select it. Only boot volumes can have permissions repaired. If the buttons labeled "Verify Disk Permissions" and "Repair Disk Permissions" are grayed and not selectable, you have not selected the boot volume or you are not a system administrator.
To allow system administrator approval to repair permissions, click on the padlock button on the lower left and enter a system administrators name and password.
Once you have selected a boot volume and have system administrator privileges, you can go ahead and click on the Repair Disk Permissions button. You will see the process begin with messages in the center window and a progress bar below it.
Once done, you can quit the Disk Utility program. You do not have to reboot the system for the changes to be effective.
For a reference to the above with screen shots please see the following link: http://www.ncmug.org/tips/repair_permissons.html