strange warning about ExtensionAttribute

Question

I\'m getting a strange warning:

The predefined type \'System.Runtime.CompilerServices.ExtensionAttribute\' is defined in multiple assemblies in the gl

Answer 1

Expanding on ShuggyCoUk's (correct) answer

Truthfully it doesn't matter which version of the attribute is used (GAC, 3rd part, etc ...). All that matters is the C#/VB compiler can find some attribute with the correct name. The attribute serves no functional purpose in code. It exists purely to tell the Compiler "hey, this is an extension method".

You can safely ignore this warning.