[C#] Compiling MONO and UE4 doesn't work. Any solutions?

I installed and built UE4 from source - everything worked perfectly. I copied the mono over and did the checkouts for creating a new branch - everything worked fine. However when I try to compile it gives me the following error:

Error 1 error CS0234: The type or namespace name ‘Linq’ does not exist in the namespace ‘System’ (are you missing an assembly reference?) f:\UE4Source\UnrealEngine\Engine\Plugins\XamarinUE4\MonoRuntime\Source\ThirdParty\mono\EmbeddedMono.Build.cs 7 14 UE4

Mention: I tried manually adding a reference to System.Linq but can’t seem to find it.

Anyone knows if I can solve this? Or should I change the import in the code to something else?

Well, you’ll need to add reference to System.Linq.dll

IMHO:
Make sure that you are using version 4.4 of the engine, and… it’s (Xamarin Mono) bugged as hell. I recommend not to use it (Many and many engine stuffs not yet implemented (and nobody knows will they ever be implemented, so… anyway it’s necessary to do most of stuffs in Cpp). Write in Cpp.

Do you have the XamarinUE4 installation package?the page was closed ,i just want to got it,thx my friend