By default, .NET 4.0 assemblies only present a Task-based pattern (TAP) asynchronous API. Please include the
Rebex.Legacy namespace in your program to make your existing code compile:
Rebex.Legacy namespace defines all the Begin/End methods as extension methods, making it possible to use to easily port your old code to newer versions of Rebex components on .NET 4.0 or higher.
This applies to versions since version 2012 R3 (build number 4700).