Have a look in your WordStar for Windows folder (by default C:\WSWIN).
In this folder you should have three font files:
- WSFONT.FON
- WSFONTE.FON
- WSFONTF.FON
If any of these are missing you need to restore them from a backup.
I think it's WSFONTF.FON that is actually causing this error message, but you should have all three in the folder.
That should fix your problem.
Regards
Mike