Extension Methods not Recognized

Question

What is necessary to have an extension method honored when it exists in an imported assembly? I built one in a class library project but it is not recognized in my web proj

Answer 1

For anyone who lands here while having the same problem in VB.NET, note that not only the extension method, but the module itself needs to be marked as Public or else you'll get this error. This is the case at least with VS2015 Community and will likely be the case in other versions too.