Junk HTML appearing at top of messages

[Ant-nee]

All,

I have a problem I've never seen before.

At the top of some of my replies, my recipients are telling me they see this:

??tml xmlns:v="urn:schemas-microsoft-com:vml"
xmlns="urn:schemas-microsoft-comfficeffice"
xmlns:w="urn:schemas-microsoft-comffice:word"
xmlns:st1="urn:schemas-microsoft-comffice:smarttags"
xmlns="http://www.w3.org/TR/REC-html40">

I also see this at the top of some sender's reply mails to me.

I do know our disclaimer software looks for HTML tags on replies so it
doesn't duplicate the disclaimer, so I figured it was the software munging
the disclaimer HTML and thereby messing up the entire HTML mail. Indeed,
after we uninstalled the software, the problem didn't happen again.

However, this problem only shows its face when people read replies that I
have sent, or when I read replies to me of mail that I have sent. The common
factor always seems to be me. No one else has reported this problem.

I am using HTML mail, Outlook 2003, and have Vista with Windows Defender and
McAfee 8.5 enabled. I don't have any viruses on the computer.

Any reason why this might happen?