Unknown Error when trying to send in HTML format

[Rob]

Windows XP Pro/Outlook 2003

I just created a signature with an image. I have set my mail format to HTML
and enabled Word 2003 as my email editor. This was working fine for several
days. But all of a sudden when I try to send the email a pop-up with the
heading 'Microsoft Office' appears stating "Unknown Error". I've looked
through Event Viewer but it doesn't log anything. If I disable Word 2003 as
my email editor it sends fine. However, it messes up the formatting of my
signature.

Thanks for your help.