Can't compile c# project because of some tuple error when referencing an external all
I have an error, when I try to build my .net 4, c# project. Everything works great, but when I add an external reference to a given DLL, it stops working, it can't build, throws this type of some errors:

Error 36 The type 'System.Tuple<T1,T2>' exists in both 'C:\Program Files\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.0\mscorlib.dll' and 'C:\Projects\Project1\ExternalRefernces\SharpSNMP\SharpSnmpLib.dll' C:\Projects\Project1\CheckerStore.cs 17 21

Note, I did not do anything with the new library, just added as a reference. Any ideas?
Can't compile c# project because of some tuple error when referencing an external all
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I have an error, when I try to build my .net 4, c# project. Everything works great, but when I add an external reference to a given DLL, it stops working, it can't build, throws this type of some errors:

Error 36 The type 'System.Tuple<T1,T2>' exists in both 'C:\Program Files\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.0\mscorlib.dll' and 'C:\Projects\Project1\ExternalRefernces\SharpSNMP\SharpSnmpLib.dll' C:\Projects\Project1\CheckerStore.cs 17 21

Note, I did not do anything with the new library, just added as a reference. Any ideas?