PCLs cannot find mscorlib

I have the following log:

1>------ Build started: Project: Nykular.Screen.Ios, Configuration: Debug Any CPU ------
1>  Nykular.Screen.Ios -> c:\dev\PetersQuest\Nykular.Screen.Ios\bin\iPhone\Debug\Nykular.Screen.Ios.dll
2>------ Build started: Project: PetersQuest.Ios, Configuration: Debug iPhone ------
2>c:\dev\PetersQuest\PetersQuest\Screens\MazeScreen.cs(31,25,31,38): warning CS0169: The field 'PetersQuest.Screens.MazeScreen._initialTouch' is never used
2>c:\dev\PetersQuest\PetersQuest.Ios\AppDelegate.cs(18,18,18,24): warning CS0169: The field 'PetersQuest.AppDelegate.window' is never used
2>  PetersQuest.Ios -> c:\dev\PetersQuest\PetersQuest.Ios\bin\iPhone\Debug\PetersQuest.exe
3>Build started.
3>Project "PetersQuest.Ios.csproj" (_RemoteBuild target(s)):
3>Target "_ComputeBundleContentPaths" in file "C:\Program Files (x86)\MSBuild\Xamarin\iOS\Xamarin.MonoTouch.Common.targets" from project "c:\dev\PetersQuest\PetersQuest.Ios\PetersQuest.Ios.csproj" (target "_PrepareApplicationBundle" depends on it):
3>Done building target "_ComputeBundleContentPaths" in project "PetersQuest.Ios.csproj".
3>Target "_GenerateBundleContentDir" in file "C:\Program Files (x86)\MSBuild\Xamarin\iOS\Xamarin.MonoTouch.Common.targets" from project "c:\dev\PetersQuest\PetersQuest.Ios\PetersQuest.Ios.csproj" (target "_PrepareApplicationBundle" depends on it):
3>Done building target "_GenerateBundleContentDir" in project "PetersQuest.Ios.csproj".
3>Target "_PrepareApplicationBundle" in file "C:\Program Files (x86)\MSBuild\Xamarin\iOS\Xamarin.MonoTouch.Common.targets" from project "c:\dev\PetersQuest\PetersQuest.Ios\PetersQuest.Ios.csproj" (target "_RemoteBuild" depends on it):
3>Done building target "_PrepareApplicationBundle" in project "PetersQuest.Ios.csproj".
3>Target "_BuildNativeApplication" in file "C:\Program Files (x86)\MSBuild\Xamarin\iOS\Xamarin.MonoTouch.Common.targets" from project "c:\dev\PetersQuest\PetersQuest.Ios\PetersQuest.Ios.csproj" (target "_RemoteBuild" depends on it):
3>Server command 'Build': application remote build failed
3>Server failure while processing the command. See below for details
3>Response status: Error
3>warning MT3005: The dependency 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' of the assembly 'Nykular.Hud, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' was not found. Please review the project's references.
3>warning MT3005: The dependency 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' of the assembly 'Nykular.Utils, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' was not found. Please review the project's references.
3>warning MT3005: The dependency 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' of the assembly 'MazeLib, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' was not found. Please review the project's references.
3>warning MT3006: Could not compute a complete dependency map for the project. This will result in slower build times because Xamarin.iOS can't properly detect what needs to be rebuilt (and what does not need to be rebuilt). Please review previous warnings for more details.
3>
3>
3>
3>Remote build step failed.
3>Done building target "_BuildNativeApplication" in project "PetersQuest.Ios.csproj" -- FAILED.
3>Done building project "PetersQuest.Ios.csproj" -- FAILED.
3>Build FAILED.
========== Build: 2 succeeded, 0 failed, 3 up-to-date, 0 skipped ==========
========== Deploy: 0 succeeded, 1 failed, 0 skipped ==========

I find this odd because Nykular.Hud, Nykular.Utils, and MazeLib are all PCLs. How do I go about debugging this?