Wrestling with my mono development environment in OS X. I had to completely remove Xamarin Studio. I don’t believe you should be opening your firewall so you could program in a windows Visual Studio IDE on another machine.
After what I think is a complete removal(uninstall) – I still get this dreaded "mtbserver allow or deny" message eveytime I try rebooting my osx portable development machine.
Anyway … I finally found that xamarin installs in this directory "/Library/LaunchAgents" this file "com.xamarin.mtvs.buildserver.plist". You got to remove this file from "/Library/LaunchAgents" this prevents launching "mtbserver".