problems sending mail "on behalf of" in office 2003 beta 2

[Johan]

Hi!

I cant send mail "on behalf of" (a public folder in this
case) from my computer with outlook 2003 beta 2.

It works just fine from my computer with outlook xp.

The same "from" address and user account used when
sending the mail.

The error message reads : "You do not have the
permissions to send the message on behalf of the
specified user"

Since I can do this from my machine with outlook xp it
shouldn't be a permissions problem.