Messenger 6 Problems - App Sharing

Messenger 6 / Zone Alarm / Alcatel Speedtouch Router - Windows XP System

Can get Audio and Web Cam connections OK between two Systems that I have.
However cannot use Application Sharing/Whiteboard or Remote Assistance.

When you select say Application Sharing, and the User at other end Accepts
the Invitation - you get the Sharing Session Windows which stays ina
"Waiting" State.

Any help will be appreciated

Alan. W