I can't open boo or js scripts in Monodevelop with a default install?

Brand new user to Unity here.

I've just installed Unity 4.5.5.f1 on Windows 7, and am trying to follow the roll-a-ball tutorial. I'm not a fan of C# so I was trying to use either js or boo, but they do not seem to be working with the default installation of monodevelop-unity.

In a brand new, blank project, I create a brand new boo script, and attempt to open it for the first time, and get the following error from monodevelop.

 An error has occurred
 
 The file 'D:\Users\Public\Documents\Unity Projects\Temp\Assets\test.boo' could not be opened. Exception has been thrown by the target of an invocation.
 
 Details
 
 System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.TypeInitializationException: The type initializer for 'Boo.Lang.Compiler.CompilerParameters' threw an exception. ---> System.TypeInitializationException: The type initializer for 'Boo.Lang.Compiler.TypeSystem.Types' threw an exception. ---> System.TypeLoadException: Could not load type 'System.Runtime.CompilerServices.ExtensionAttribute' from assembly 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.
    at Boo.Lang.Compiler.TypeSystem.Types..cctor()
    --- End of inner exception stack trace ---
    at Boo.Lang.Compiler.TypeSystem.Reflection.ReflectionTypeSystemProvider.ObjectTypeImpl..ctor(IReflectionTypeSystemProvider provider)
    at Boo.Lang.Compiler.TypeSystem.Reflection.ReflectionTypeSystemProvider..ctor()
    at Boo.Lang.Compiler.CompilerParameters..cctor()
    --- End of inner exception stack trace ---
    at Boo.Lang.Compiler.CompilerParameters..ctor()
    at Boo.Lang.Compiler.BooCompiler..ctor()
    at Boo.MonoDevelop.ProjectModel.BooParser..ctor()
    --- End of inner exception stack trace ---
    at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck)
    at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache)
    at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean skipCheckThis, Boolean fillCache)
    at System.Activator.CreateInstance(Type type, Boolean nonPublic)
    at Mono.Addins.TypeExtensionNode.CreateInstance() in c:\BuildAgent\work\d478831d940d36a4\monodevelop\main\external\mono-addins\Mono.Addins\Mono.Addins\TypeExtensionNode.cs:line 93
    at MonoDevelop.Ide.TypeSystem.TypeSystemParserNode.get_Parser() in c:\BuildAgent\work\d478831d940d36a4\monodevelop\main\src\core\MonoDevelop.Ide\MonoDevelop.Ide.TypeSystem\TypeSystemParserNode.cs:line 63
    at MonoDevelop.Ide.TypeSystem.TypeSystemService.GetParser(String mimeType, String buildAction) in c:\BuildAgent\work\d478831d940d36a4\monodevelop\main\src\core\MonoDevelop.Ide\MonoDevelop.Ide.TypeSystem\TypeSystemService.cs:line 282
    at MonoDevelop.SourceEditor.SourceEditorView.RunFirstTimeFoldUpdate(String text) in c:\BuildAgent\work\d478831d940d36a4\monodevelop\main\src\addins\MonoDevelop.SourceEditor2\MonoDevelop.SourceEditor\SourceEditorView.cs:line 742
    at MonoDevelop.SourceEditor.SourceEditorView.Load(String fileName, Encoding loadEncoding) in c:\BuildAgent\work\d478831d940d36a4\monodevelop\main\src\addins\MonoDevelop.SourceEditor2\MonoDevelop.SourceEditor\SourceEditorView.cs:line 819
    at MonoDevelop.SourceEditor.SourceEditorView.Load(String fileName) in c:\BuildAgent\work\d478831d940d36a4\monodevelop\main\src\addins\MonoDevelop.SourceEditor2\MonoDevelop.SourceEditor\SourceEditorView.cs:line 729
    at MonoDevelop.Ide.Gui.LoadFileWrapper.Invoke(String fileName) in c:\BuildAgent\work\d478831d940d36a4\monodevelop\main\src\core\MonoDevelop.Ide\MonoDevelop.Ide.Gui\Workbench.cs:line 1201

Likewise when I do the same with a javascript file I get the following error:

 An error has occurred
 
 The file 'D:\Users\Public\Documents\Unity Projects\Temp\Assets\test.js' could not be opened. The type initializer for 'Boo.Lang.Compiler.TypeSystem.Types' threw an exception.
 
 Details
 
 System.TypeInitializationException: The type initializer for 'Boo.Lang.Compiler.TypeSystem.Types' threw an exception. ---> System.TypeLoadException: Could not load type 'System.Runtime.CompilerServices.ExtensionAttribute' from assembly 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.
    at Boo.Lang.Compiler.TypeSystem.Types..cctor()
    --- End of inner exception stack trace ---
    at Boo.Lang.Compiler.TypeSystem.Reflection.ReflectionTypeSystemProvider.ObjectTypeImpl..ctor(IReflectionTypeSystemProvider provider)
    at Boo.Lang.Compiler.TypeSystem.Reflection.ReflectionTypeSystemProvider..ctor()
    at UnityScript.UnityScriptCompilerParameters..ctor(Boolean loadDefaultReferences)
    at UnityScript.UnityScriptCompilerParameters..ctor()
    at UnityScript.UnityScriptCompiler..ctor()
    at UnityScript.MonoDevelop.ProjectModel.UnityScriptParserModule.ParseUnityScript(String fileName, String content)
    at UnityScript.MonoDevelop.ProjectModel.UnityScriptParser.Parse(Boolean storeAst, String fileName, TextReader reader, Project project)
    at MonoDevelop.SourceEditor.SourceEditorView.RunFirstTimeFoldUpdate(String text) in c:\BuildAgent\work\d478831d940d36a4\monodevelop\main\src\addins\MonoDevelop.SourceEditor2\MonoDevelop.SourceEditor\SourceEditorView.cs:line 734
    at MonoDevelop.SourceEditor.SourceEditorView.Load(String fileName, Encoding loadEncoding) in c:\BuildAgent\work\d478831d940d36a4\monodevelop\main\src\addins\MonoDevelop.SourceEditor2\MonoDevelop.SourceEditor\SourceEditorView.cs:line 819
    at MonoDevelop.SourceEditor.SourceEditorView.Load(String fileName) in c:\BuildAgent\work\d478831d940d36a4\monodevelop\main\src\addins\MonoDevelop.SourceEditor2\MonoDevelop.SourceEditor\SourceEditorView.cs:line 729
    at MonoDevelop.Ide.Gui.LoadFileWrapper.Invoke(String fileName) in c:\BuildAgent\work\d478831d940d36a4\monodevelop\main\src\core\MonoDevelop.Ide\MonoDevelop.Ide.Gui\Workbench.cs:line 1201
 

But I can do the same with a C# script and it works just fine! What gives? Is there something wrong with the default installation? Is there anything I can do to fix this?