If clients are XP SP2, check kba 883543 and apply the hotfix.
Pre-XP SP2 clients: reinstall the S/MIME control from OWA - options.

Signature
Bharat Suneja
MCSE, MCT
www.zenprise.com
blog: www.suneja.com/blog
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>I have an exchange 2003 server that for one user is adding a '?' to the
> first line in each message she sends from OWA. This doesn't happen
> with Outlook, nor does it happen with OWA on any other client, it seems
> to be from her laptop only that is having the problem. I noticed one
> other post about this in here, but it was from almost a year ago and no
> reply was ever sent. How do I fix this?