Can no longer build an old project in Xamarin

I have an old project that used to build

However I have recently tried rebuilding since a xamarin update it and I get an error message

The name 'Build' does not exist within the current context.

I've tried building it with different versions of the .net framework

but none of these have worked.

I have also noticed the warning message

Warning MSB3276: Found conflicts between different versions of the same dependent assembly. Please set the "AutoGenerateBindingRedirects" property to true in the project file.

It looks like I might be building it with the wrong assembly version.

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EDIT

I've checked the GTK version and there is only one option in my case. Version 2.12

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EDIT

I've just tried restoring my code from version control.

My project will build! ... But I have not really fixed the problem since I get the following runtime error.

System.DllNotFoundException: Unable to load DLL 'libgtk-win32-2.0-0.dll': The specified procedure could not be found. (Exception from HRESULT: 0x8007007F)

Which tells me that I haven't built it with libgtk-win32-2.0-0.dll.

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EDIT

I've just created a simple test program after reinstalling Xamarin

When I built it the first time I get the same message about "AutoGenerateBindingRedirects"

When I built it again I get a different error message.

System.DllNotFoundException

I'm back to not being able to find libgtk

I have finally got it working. Here's what I did

I uninstalled all xamarin, mono and GTK programs from windows using the windows control panel.

Removed all registry entries I could find.

Manually deleted the remaining program files from my hard drive.

Went and downloaded the latest versions of GTK and mono and .net. Reinstalled and rebooted.

Copied the gtk files into my program directory and everything worked.

I'm not sure which of these steps may have helped.