Well, I'm asking this question on behalf of my friend. He's using Windows Vista Ultimate and MS Office Word 2003. (I'm on XPSP2 anyway, don't have that luxury to upgrade anytime soon..)
The problem was that my friend has this one word document in his usb flash drive. After he has done some editing with his word document and try to save it, the error messages "Word cannot complete the save due to a file permission error" prompted into his screen. He soon discovered that the file was deleted from the flash drive whenever he try to save the file directly to flash drive.
He also tried to duplicate the scenario and he got the same problem over and over again. His word documents keep on disappearing or deleted for that 'file permission error' reason.
The only workaround that i've found for this problem was, do the editing in the harddrive first and then 'move-and-paste' the file to the thumbdrive afterward. Now, this somehow works for him.
There is no other security related apps installed in his machine beside Avast! Antivirus Home Edition.
Any ideas ?
