XamlFiles parameter is not supported by XamlGtask

Update:

After some more searching around I came upon this github thread dealing with the exact same issue: https://github.com/xamarin/Xamarin.Forms/issues/2975.

I updated my android packages and changed the target to the latest version, cleaned the solution and restarted the IDE and that worked.

If anybody, however, can explain what the error means, that would be much appreciated.

I also have this error. However, I had already update the Xamarin.Forms in Nuget. The error still occurred.

After a few hours searching and trying, I opened the .csproj file by external code editor and found some lines that import different version of Xamarin.Forms

<Import Project="..\packages\Xamarin.Forms.2.3.3.193\build\portable-win+net45+wp80+win81+wpa81+MonoAndroid10+Xamarin.iOS10+xamarinmac20\Xamarin.Forms.targets" Condition="Exists('..\packages\Xamarin.Forms.2.3.3.193\build\portable-win+net45+wp80+win81+wpa81+MonoAndroid10+Xamarin.iOS10+xamarinmac20\Xamarin.Forms.targets')" />
.....
<Import Project="..\packages\Xamarin.Forms.3.5.0.129452\build\Xamarin.Forms.props" Condition="Exists('..\packages\Xamarin.Forms.3.5.0.129452\build\Xamarin.Forms.props')" />
<Import Project="..\packages\Xamarin.Forms.3.5.0.129452\build\Xamarin.Forms.targets" Condition="Exists('..\packages\Xamarin.Forms.3.5.0.129452\build\Xamarin.Forms.targets')" />

And somethings like this

<Error Condition="!Exists('..\packages\Xamarin.Forms.2.3.3.193\build\portable-win+net45+wp80+win81+wpa81+MonoAndroid10+Xamarin.iOS10+xamarinmac20\Xamarin.Forms.targets')" Text="$([System.String]::Format('$(ErrorText)', '..\packages\Xamarin.Forms.2.3.3.193\build\portable-win+net45+wp80+win81+wpa81+MonoAndroid10+Xamarin.iOS10+xamarinmac20\Xamarin.Forms.targets'))" />
<Error Condition="!Exists('..\packages\Xamarin.Forms.3.5.0.129452\build\Xamarin.Forms.props')" Text="$([System.String]::Format('$(ErrorText)', '..\packages\Xamarin.Forms.3.5.0.129452\build\Xamarin.Forms.props'))" />
<Error Condition="!Exists('..\packages\Xamarin.Forms.3.5.0.129452\build\Xamarin.Forms.targets')" Text="$([System.String]::Format('$(ErrorText)', '..\packages\Xamarin.Forms.3.5.0.129452\build\Xamarin.Forms.targets'))" />

So. I decided to remove all lines that contains old version of Xamarin.Forms. Then, Reload the project Clean and Build again.

The error disappeared!