All of a sudden, with no changes to options etc. ALL of my spreadsheets can
NOT be saved!

I get the message 'Your changes could not be saved to {filename.xls}'
because of a sharing violation. Try saving to a different file."

If I do that, it saves it to a file name composed of a letter and several
numbers but leaves the original file open. If I close the original and Save
As from the new file to the old name I get the message 'The file
'{filename.xls}' may have been changed by another user since you last saved
it. In that case, what do you want to do?'

I am then given 2 choices Save a Copy (default choice) or Overwrite the
changes. I logically choose the second option in which case I ALWAYS get the
error message 'Document not saved'.

If I then close the file, reopen it and save as it saves correctly.

THIS IS ANNOYING and time consuming. The files have never been shared and
are not presently shared.

I have done a detect and repair on Excel and all other Office 2003
applications but nothing changes.

HOW do I stop this annoyance from happening?