We're having the same issue, though it only seems to happen on around 5% to 10% of our email templates. 

- We've noticed that Outlook 2003 displays the emails fine, but Outlook 2000 is insering random exclamation marks.

- When we forward the email from the Outlook 2000 clients to Outlook 2003 then the exclamation marks are still present,

- When we forward from the Outlook 2003 clients to the Outlook 2000 then the email appears with no issues.

(I'm currently updating from CuteSoft editor 5.2 to 6.0 to see if this fixes the issue)