InfoPath 2007 Email Data Connection Fails

Question

We have an InfoPath 2007 form that has an email submit data connection. This works for all clients that use the form but one. That one client has Office 2007 and if I create a simple XSN that only has one button which submits via an email data connection that works. So, the form works for all clients, but one - and a simple email submit works for that one client.

When things do not work the send email dialog does not pop up at all.

Any ideas? Is there any way to get a log/trace of issues?