There might be many reasons behind this error :
1. Faulty synchronization of OST & Exchange
2. Unauthorized Login Attempts
3. Multiple Users Login Attempts at the same time
4. Internet Connection Errors
There are 2 methods to Repair OST File :
1.) Inbuilt Inbox Repair Tool
Outlook provides an inbuilt Utility ScanOST.exe also known as OST Integrity Check to repair OST File
2.) Disabling Cached Exchange Mode
OST file is automatically created when Cached Exchange Mode is turned on. So turning it off might solve the issue.
a.) Go to Control Panel -> Mail -> Email Accounts
b.) Choose Change
c.) Uncheck "Use Cached Exchange Mode"
Hopefully, this will help you resolve the issue.
Thanks & Regards,