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Background & Issue
I am setting up a CI build in Visual Studio Online (VSO) for a Xamarin project as part of research for some docs and blog posts. I set up a simple solution with a Xamarin.Android app and a UITest project with one automated test.
Everything works find on my local developer workstation which is a VMware Fusion image running Windows 10, Visual Studio 2015 Pro, and Xamarin 3.11.836.
When I run the build in Visual Studio Online, the build fails with the error :
2015-08-20T16:39:01.2412835Z 1>CSC : error CS1703: Multiple assemblies with equivalent identity have been imported: 'C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\MonoAndroid\v1.0\mscorlib.dll' and 'C:\Windows\Microsoft.NET\Framework\v4.0.30319\mscorlib.dll'. Remove one of the duplicate references. [C:\a\a815ee8d\phoneword\PhonewordAndroid\PhonewordAndroid.csproj]
I logged this as an issue against the VSO Agent Tasks, https://github.com/Microsoft/vso-agent-tasks/issues/439, and eventual made contact with a developer from Microsoft about this issue. The problem seems to be that VSO has a slightly older version of Xamarin installed in their images, they have Xamarin 3.11.666 (released August 5th?) installed. When Microsoft upgraded to the most recent version of Xamarin for Windows, the Xamarin.Android build task could successfully compile the project.
Currently the workaround from Microsoft is that only should fall back to the older version of Xamarin for Windows (3.11.666) as not all data centres will immediately receive the upgraded Xamarin.
An older version of Xamarin for Windows should be able to compile and package a Xamarin.Android project even if the .CSPROJ file was edited by a newer version of Xamarin/Visual Studio.
Just tried this again with Xamarin 3.11.1443. It seems that the Xamarin tasks for VSO build the project just fine.
I have confirmed with Microsoft that they have not updated their VSO with a new version of Xamarin. They are still running 3.11.666.
The problem seems to have gone away in more recent builds of Xamarin for Visual Studio (3.11.1443 or higher). Closing this issue off.