Try to repair your pst file. Follow these steps:
1. Exit Outlook if it is running.
2. Double-click Scanpst.exe, located at drive:\Program Files\Microsoft Office\OFFICE12.
3. In the Enter the name of the file you want to scan box, enter the name of the .pst or .ost file that you want to check, or click Browse to search for the file.
4. To specify the scan log options, click Options, and then click the option that you want.
5. Click Start.
If errors are found after the scan is complete, you will be prompted to start the repair process to fix the errors.
A backup file is created during the repair process. To change the default name or location of this backup file, in the Enter name of backup file box, enter a new name, or click Browse to look for the file that you want to use.
7. Click Repair.
8. Start Outlook by using the profile that contains the .pst file that you tried to repair.
9. On the Go menu, click Folder List.
In the Folder List, you may see a folder named Recovered Personal Folders that contains your default Outlook folders or a Lost and Found folder. The recovered folders are usually empty, because this is a rebuilt .pst file. The Lost and Found folder contains the folders and items recovered by the Inbox Repair tool. Items that are missing from the Lost and Found folder cannot be repaired.
10. If you see a Recovered Personal Folders folder, you can create a new .pst file, and drag the items in the Lost and Found folder into the new .pst file. When you have finished moving all the items, you can remove the Recovered Personal Folders (.pst) file, including the Lost and Found folder, from your profile.