If the "Atttach BIG-IP" workflow is failing, consider the following actions:
1. Make sure the hostname/IP Address resolve properly and can be pinged from the vRO system.
2. Ensure that the username and password are correct.
3. Consider changing the "Max Threads" value to a lower number. It is possible that too many calls are causing the endpoint to not return from the API. (A good example would be 5 threads.)
If you have gone through the above steps and are still unable to attach the BIG-IP system, please open up a support ticket with VMware.