From email: I'm not sure if this an issue but still: solution-wide analysis reports a failure if there is an extension method but there are no references to System.Core (I guess there could be the same story with Linq). Although, that's not a bug. My VS projects target .NET 2.0 and I use LinqBridge to keep the compiler happy without the System.Core (See http://rabdullin.com/how-to-use-net-35-syntax-and-compiler-features-for-net-20/ for the details). The suggestion is to check for any valid extension marker attribute intead of simply checking the reference to System.Core