TLDR version: install xcode on your Mac, since it is probably not installed.
Today I spend about an hour getting things up and running because I kept running into problems getting visual studio to pair with the build host.
This is one of the things that you need to set up when you want to build iOS applications with Xamarin and Visual Studio, is the build host that runs on a Mac.
I had installed Xamarin studio on my MacBook and windows running in Parallels. Started the build host and then clicked the button to pair, giving me a PIN number to use to pair Visual Studio with the build host.
But the Visual Studio pairing dialog kept telling me the PIN number was incorrect, even after copying and pasting it from the build host control into the connection dialog.
When running Diagnostics I saw it kept failing on connecting to the build host. Connectivity to the mac was ok, but the build host could not be reached. I tried of course many things, turning of the fire wall being e.g. one of the things I tried.
When looking at the details, I kept getting the diagnostics failing with a cryptic message. The message was:
Parameter name: must be between 0 and 65535
Almost ready to pull my hair out I got one moment of enlightenment. What I did is that I started xamarin studio on my MacBook and there tried to build an iOS app. Just to see if I could build an app and run it in the simulator, just to ensure all is good on the Mac side.
Then I tried to build the app and run it in the simulator and I got the message that XCode was not installed. And that was true, it is a brand new MacBook and after installing Xamarin I just went straight through installing the visual studio side of thing.
After installing XCode and checking I could run a simple app in the simulator, I tried reconnecting the Visual Studio environment again and voila, problem solved.
So if you get the message Parameter name: must be between 0 and 65535, chances are you haven’t fully installed everything required to run an app in the iOS simulator.
Hope that helps,