Hi
Try these steps:
1. Turn on the Show/Hide function which is on the Home tab about half way along the screen.
2. Enter Ctrl+A to select the whole document.
3. Enter Ctrl+Shift+Left Arrow - this has the effect of deselecting the very last paragraph mark in your document which contains most of the formatting for the whole of the document.
4. Enter Ctrl+N to create a new document.
5. Try and save the document then.
Let me know if this works.
Good luck.
Tony