You see this error message in the Qbwin.log file:
Error: Failed to decrypt user's master key. UserID: 0. Error: Failed to decrypt user's data access key
The User List or your built-in admin user in your company data file is damaged.
This step is very important: Close out of the company file (File- Close Company/Log off), then close the program completely, then log back in as the Admin user. This will finish the re-encryption process.