See the question and my original answer on StackOverflow

If referencing System.Web.dll is not an issue for you, there is the little-known BuildManager.GetType Method which is quite efficient. It does not even requires the assembly name because it scans for types in assemblies in the current AppDomain execution path.

So the code would be:

object instance = Activator.CreateInstance(BuildManager.GetType("MyNamespace.MyClass", true));