Error -50


With may editor (Text Edit Plus, Pepper, Graphic Converte...) an error -50 occurs when I try to save for the second time a document.
I open a new blank page, write something and save (OK), write something other and save (Error -50!!!).
I've noticed this problem only if I save the document on the unix osx partition, on the mac os extended secondary partition of os 9.1 I can save and resave with no problems.

Sorry for bad english. What can I do?