MS Word problems

[JROK]

I've been having problems with MS Word 2007 when I go to save files. Every so often when I go to save a file an error message pops up: "Word cannot complete the save due to a file permission error" My only option on the error message is to click "OK" Sometimes another errors message pops up after this and then Word shut down. Other times after I click OK Word is fine. However, after this first error message appears my original file disappears completely from the location I had it saved (e.g. flash drive). A hidden temporary file appears in its place with the name "~WRLXXXX.tmp" If the Word closes down, I just open this temporary file and only lose stuff after the previous save point.

Why is this happening?