I've seen this message before, and typically it has to do with an error communicating with the domain controller, but in this situation that is not the case. I currently get this even when the machine is not joined to a domain. I have tried uninstalling and reinstalling UAG a number of times, but it doesn't change. I started digging further into TMG and discovered that when I click on "Networking" or when I click on the System<Servers<Servername<Properties<Communication tab (where you set the Intra-Array IP address) I get the following error:
Forefront TMG cannot load the property page. Error 0xc004045f The default gateway for the specified network adapter is on its upper or lower subnet boundary. The error occurred on object 'SERVERNAME' of class 'Server' in the scope of array 'SERVERNAME.'
I can't find any information on this error, sound familiar to anyone here?
Well, in this situation the error message meant exactly what it said - that the specified default gateway was on its subnet boundary. Specifically, the client had supplied me with IP address information and it turns out the default gateway for the external network was the Subnet ID address of that subnet, not one of the "usable" IPs in that subnet. While technically this configuration is supported at a network level (I could still get to the internet through that default gateway), TMG no likey.
So once we configured a router on the subnet to also gateway traffic out to the internet and pointed the default gateway of this machine to that router, TMG was happy...and as soon as I made that change the UAG management console opened without a problem as well.