After reading how you switched to .NET 4.0, I tried running this in Mono on Linux for the heck of it (seeing as I'm very interested in this becoming a cross-platform thing). It actually gets past the initial WinForms dependencies (once installed)! But it still errors out in a few ways:
Missing method System.Type::op_Equality(Type,Type) in assembly /usr/lib/mono/2.0/mscorlib.dll, referenced in assembly /usr/lib/mono/gac/UIAutomationProvider/3.0.0.0__31bf3856ad364e35/UIAutomationProvider.dll
Error setting up UIA: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.TypeInitializationException: An exception was thrown by the type initializer for System.Windows.Automation.Provider.AutomationInteropProvider ---> System.MissingMethodException: Method not found: 'System.Type.op_Equality'.
at System.Windows.Automation.Provider.BridgeManager.GetAutomationBridges () [0x00000] in <filename unknown>:0
at System.Windows.Automation.Provider.AutomationInteropProvider..cctor () [0x00000] in <filename unknown>:0
--- End of inner exception stack trace ---
at Mono.UIAutomation.Winforms.FormListener.Initialize () [0x00000] in <filename unknown>:0
at Mono.UIAutomation.Winforms.Global.Initialize () [0x00000] in <filename unknown>:0
at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0
--- End of inner exception stack trace ---
at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0
at System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) [0x00000] in <filename unknown>:0
at System.Windows.Forms.Application.InitializeUIAutomation () [0x00000] in <filename unknown>:0
Fontconfig warning: "/etc/fonts/conf.d/50-user.conf", line 9: reading configurations from ~/.fonts.conf is deprecated.
Unhandled Exception: System.TypeInitializationException: An exception was thrown by the type initializer for System.Windows.Forms.XplatUI ---> System.TypeInitializationException: An exception was thrown by the type initializer for System.Windows.Automation.Provider.AutomationInteropProvider ---> System.MissingMethodException: Method not found: 'System.Type.op_Equality'.
at System.Windows.Automation.Provider.BridgeManager.GetAutomationBridges () [0x00000] in <filename unknown>:0
at System.Windows.Automation.Provider.AutomationInteropProvider..cctor () [0x00000] in <filename unknown>:0
--- End of inner exception stack trace ---
at Mono.UIAutomation.Winforms.FormListener.Initialize () [0x00000] in <filename unknown>:0
at Mono.UIAutomation.Winforms.Global.Initialize () [0x00000] in <filename unknown>:0
at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0
--- End of inner exception stack trace ---
at System.Windows.Forms.Application.EnableVisualStyles () [0x00000] in <filename unknown>:0
at Sphere_Editor.Program.Main () [0x00000] in <filename unknown>:0
[ERROR] FATAL UNHANDLED EXCEPTION: System.TypeInitializationException: An exception was thrown by the type initializer for System.Windows.Forms.XplatUI ---> System.TypeInitializationException: An exception was thrown by the type initializer for System.Windows.Automation.Provider.AutomationInteropProvider ---> System.MissingMethodException: Method not found: 'System.Type.op_Equality'.
at System.Windows.Automation.Provider.BridgeManager.GetAutomationBridges () [0x00000] in <filename unknown>:0
at System.Windows.Automation.Provider.AutomationInteropProvider..cctor () [0x00000] in <filename unknown>:0
--- End of inner exception stack trace ---
at Mono.UIAutomation.Winforms.FormListener.Initialize () [0x00000] in <filename unknown>:0
at Mono.UIAutomation.Winforms.Global.Initialize () [0x00000] in <filename unknown>:0
at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0
--- End of inner exception stack trace ---
at System.Windows.Forms.Application.EnableVisualStyles () [0x00000] in <filename unknown>:0
at Sphere_Editor.Program.Main () [0x00000] in <filename unknown>:0