Regarding the error, it may occur if the user has port 1935 closed in their or their company's firewall; they need to open it. This is quite normal in places with many security restrictions. The user must solve it with their company or in the place they are connecting from.
Documented by Adobe: Error: FMS Server did not return correctly! This error is sometimes seen on County networks or other networks with strict firewall policies. To resolve this, open up port 1935 for the meeting. Request the Connect server IP address if necessary.