Frozen Remote Desktop Image

I am attempting to connect to the Ubuntu Remote Desktop from a Windows XP computer using RealVNC. RealVNC connects and displays the Ubuntu Desktop correctly, however the image is then frozen. For example if I click on a menu item or attempt to open application from an item on the RealVNC desktop, the Ubuntu image remains unchanged. However when I physically look at the Ubuntu computer the menu or application has actually responded to the remote request.

The connection is running across a LAN, no firewalls or third party applications are interfering with the connection

Unsure if this is issue with Ubuntu or RealVNC. Have used RealVNC extensively in the past without issue. Any Suggestions?