Microsoft Outlook pst is also referred to as Personal Folders file. This is repository file of Outlook that stores all your Outlook data including emails, notes, calendars, appointments, journals, contacts etc. Outlook pst file has limited size i.e. it can't exceed its size from 2GB. Therefore it is recommended to make backup of the pst file and use new pst file in case the pst file size approaches 2GB. If you use the oversized pst file in Outlook, then it may get corrupted and all the data will get lost. But many of the users have encountered problem in accessing the old one pst file. When you try to import data from the previous .pst file, you receive "Outlook.pst is not a Personal Folders file" error message in Outlook.
Sometime you may also encounter the error "Outlook.pst is not a Personal Folders file" when you try to start Outlook 2007 on Windows 7. When the error occurs, the program couldn't open. This is the major error in Outlook and it must be resolved immediately. Typically, Outlook.pst error appears due to corruption in the file. If you encounter the error while importing data from another pst file then the file may be set to Read-Only. Therefore, you should first make sure that the file is not Read-Only. In order to remove Read-Only attribute from the file follow the steps:
Now again you try to import the pst file. In case, you still receive the same outlook personal folders file error then you will need to use Inbox Repair tool to repair the file. If this utility fails to repair and produce error like "Inbox Repair Tool does not recognize the file. [path/Outlook.pst]. No information can be recovered." then the pst file is severely corrupted. In this situation, you are required to repair with professional Outlook PST Repair Tool. The software successfully repairs any oversized or corrupted outlook.pst file. It also recovers the lost or missing outlook items from the pst file.