To fix this issue, go through following instructions:
1: Open Task Manager on your System
2: Now click on the process mentioned on the Top
3: Locate Outlook.exe and click right and End the process
4: Now make sure that there is no Outlook.exe is open if open the end the process to run the ScanPST
5: Then run ScanPST.exe and scan your PST file.
If the problem still exists, then try ScanPST.exe alternative like Stellar Phoenix Outlook PST Repair. Users can download its free demo from: http://www.stellaroutlooktools.com/scan/pst-repair.php