Here's the error code:
FRM-91111: Internal Error: window system startup failure.
FRM-10039: Unable to start up the Form Builder.
It should work right out of the box, looks like the build config had changed much, here's the env file used:
Eventually found this documentation post about how to solve the problem. Basically since the last time we used forms builder on this server, the other Oracle homes required a change to NLS_LANG with a UTF8 characterset.
Simply added the following to the above forms builder env file fixed the issue with forms builder: