E-mails are changed to .asp files!

There is one user here who is experiencing a problem, and he alone is experiencing it. Sometimes, Word or Excel files get turned into .asp files! You can read the text, but embedded in it is the outlook screen itself, with all of the command buttons(Reply, Reply to All, Save, etc)turned into JavaScript functions.

The funny thing is, it doesn't happen every time. Also strange is that some of the files are mass-e-mail for the whole company, and we all get them fine.

Any idea what is causing this and what can be done to fix it?

Thanks!

+Melanie-