As you're seeing 'Access Denied' it seems like there is a security policy in place preventing access. Is there another access rule in TMG that may be overriding the Fastvue rule? Or perhaps there is another device between the two servers that could be preventing access? Open a command prompt and enter tracert <IP address of your TMG Server>. This will show you the 'hops' between you and the server to give you an idea.
As a test, try disabling the Windows Firewall on the Fastvue server. If that works, you can re-enable Windows firewall but add an exception for the 'Fastvue TMG Reporter' service, or port 49361.
I'm assuming 'TMGServer' is the actual name of your server and that is resolving correctly from the Fastvue TMG Reporter machine? As a test, can you delete the source and add it again, but using the IP address of your TMG Server?
The best way to check that the Fastvue TMG Reporter server can access the Fastvue Arbiter on your TMG Server is to open a Telnet session from the Fastvue Server to the TMG Server on port 49361.
To do this: 1. Install Telnet if it isn't already. Go to Programs and Features | Turn Windows Feature on or off 2. Check 'Telnet Client' and click OK. 3. Open a command prompt (Start | Run | cmd) and type Telnet 4. Then type: open <ip address of TMG Server> 49361 e.g. open 10.0.0.1 49361