In the message shown below, the part that says "error when keeping" probably
should be "error when saving". It is logical that there might be an error
saving an attachment. It is not logical that Windows Mail would say it
(whatever it is) "verifies the free disc space", so whatever the message
does say seems to have been lost in translation.
If your Vista does not have all updates from Windows Update, you should get
your system updated; that might solve the problem you are having with
attachments.