I would setup a webex type session with the customer and see if you can remote control the session to login using the same credentials and see if it launches from the internal network.
If that works then you can work with their network folks to enable the external access you need or perhaps they can provide a vpn connection when you need to access the config panel.
If it doesn't launch internally you will need to have their SAP team figure out why it is not launching.
--Bill