Microsoft provides the Inbox Repair Tool for correcting most problems with damaged Personal Folders .pst files. If you do not see the Inbox Repair Tool on the Start menu, under Programs | Accessories | System Tools, use Start | Find or Start | Search (depending on your operating system) to search your system for Scanpst.exe.
You will need to know the location of the .pst file that you want to repair. See Outlook & Exchange/Windows Messaging Backup and Dual-Boot for information on file locations and ways to determine the location of a .pst file that you can see in Outlook.
“.pst is not a personal folder file” the error message indicates the corruption in Outlook PST file. Outlook PST file corruption is the reason of this error and
Necessary actions are required for repairing the Outlook data file. You also create new PST file, but you want old file because file contained all important emails so you can use Microsoft Inbox Repair tool Scanpst.exe to repair PST file. Scanpst.exe is the inbuilt utility to scan and repair corrupt PST file.