To close this out, the problem is solved but still a mystery. There were *two* APWIN.INI files in the APWIN folder. One was spelled APWIN.INI and the other APWIN.ini. I don't know how Windows keeps two files with the same name but different extension case in the same folder but I saw it myself.

One was damaged. I deleted it. Payables came back to life.

Why were there two files? I don't know.