Been a while since I used Jamba, but I will ask the standard sort of troubleshooting questions I would want as a developer. Best case, they solve it; worst case it save Ebony having to ask similar things.

Do you have the latest version of the addon and/or dependencies?
Are you in a flying area and don't have flying for there? Can you manually mount with the mount in the Jamba setup?
Are you using a keybind to activate it, and are you sure that your modifier key setup is correct? Have you tried the command in the console?
Do you know if the command takes any arguments?
Are there any errors or other indicators it is having a problem, or are there any sounds or other things that indicate it succeeded?
Do you have any other addons that provide any mount features or might interfere or change mounting?

Once again, I'm sorta taking a shot in the dark. Hope I didn't waste anytime, but maybe these will trigger something that solves it.

- Souca | Clueless as Always