Please make this go away... 16 bit windows subsystem message problem?

When I log on my computer I get this message every time for the past few months. "16 bit windows subsystem - An application has attempted to directly access the hard disk, which cannot be supported. This may cause the application to function incorrectly, chose close to terminate the application." Then it gives two choices "close" or "ignore". I've clicked on both choices at different times with no difference in effect. I obviously don't understand what is causing this and how to stop it. This is an older Compaq Presario 344mhz? 10 gig 128RAM Windows XP Professional Operating System. It is quite slow, I'm on dial up. I plan on replacing it soon. I have a routine weekly schedual to run updates from Microsoft, AVG Free Edition virus protection, AdAware6 free edition, I'm not sure if this is successful? I recently purchased and ran RegCure, it found thousands of things to fix, things do run a little faster now. However, this 16 bit windows subsystem message continues.