Some DOS programs stopped working

[dtamonis]

I've got a strange problem. Many DOS programs, including command.com, recently stopped working. When I execute them, I get an illegal operation error: screenshot. Fault location is always the same.

This does not affect all DOS programs, some of them work fine, but this error still appears when I break them with Ctrl+Break. I remember that everything was fine on January 2nd, so I restored a registry copy of December 31st (with scanreg), that didn't help.

Tried searching the net, but the only solution that helped someone was to disable the antivirus protection. I do not have antivirus installed at all.

Any ideas?

[jds]

I do not have antivirus installed at all.

That's funny, the first thing that came to my mind, is that you should scan for nasties.

If that's not the problem, check (no, I'm not sure how) that %windir%\system\conagent.pif and %windir%\pif\command.pif (and there may also be a '_default.pif' and several 'MS-DOS Prompt.pif' files somewhere) aren't corrupted.

Joe.

[dtamonis]

I don't use AV for years, and no problems with malware. Anyway, I checked the PIFs, didn't find anything I could suspect, just to be sure scanned the system partition with Drweb CureIt (it took forever), and then just copied all the files (except hidden or system) from the backup copy of Windir and System folders, ovewriting the existing ones. Problem solved, so thanks for the idea about corrupt files.