Java Client

A customer has a single Citrix XenApp 4.5 server with WI installed on this Citrix server. They are not running CSG and they do not have a CAG. The Java client has been installed successfully and WI works fine inside the LAN with the Java client. Port 443 and port 1494 have been opened in the NAT firewall. When a user accesses the external IP address of the firewall to get to WI, all seems well. Credentials are accepted and published application icons are displayed in the WI. However when an application is clicked on, the Java client launches but the connection to the published app is never established. How do you troubleshoot this situation. What are the most likely culprits?