The work file is a temporary file that Word wants to create but isn't creating on your computer for some reason. It uses that file to store the actions you take while working on that document. It's what allows you to click "undo" for example, in order to undo the last action you took on the document. If Word can't create that file, it's going to try and force you to save your document over and over and over again.

If the message you're getting is telling you don't have that work file and that you're out of memory, and then leaves you no other option than to save your work, this is probably what the problem is.

I used to see this error a lot at my work, usually with Word 2003 running XP machines but it has been years since I've seen it. I offer no guarantees because it's been a long time but you might be able to fix this by either

With Word closed and not running...Going to the Run prompt (hit Windows key and R key at the same time, I think if you use Vista), type "winword.exe /r" (without the quotes but with the space between the e and slash), hit enter and then test to see if it worked or;

Re-installing Word.

Hope this helps.