The Sage 50 ini file is corrupted.

Section 1

1. Go to C:\Users\%username%\AppData\Local\Simply Accounting\
    NOTE: If you don't see AppData, click on View at the top and check the box for Hidden items.
2. Delete ALL the .ini files.
   For example: simply310 is the .ini file for version 2024.
3. Open Sage 50 again. If you're still getting an error go to Section 2.

Section 2

1. Go to C:\Users\%username%\AppData\Local\Simply Accounting\ 
2. Delete the location path after Data file =.
3. Save and close the .ini file.
4. Open Sage 50 again.
5. If the error still comes up, rename the Simply Accounting folder to Simply Accounting Old.
6. Run repair.

As an alternative to running repair, the Simply Accounting folder can be replaced by a Simply Accounting folder from another computer.

Modifying the simplyXXX.ini file can also fix the issue by opening simply file, the file name format comes up with *.asc, *.sdb, etc in the "File name" field.