Dotnetnuke 6.x and Ajax Control Toolkit
Ajax Control Toolkit (ACT) is commonly used control library among ASP.NET Webforms projects; much more used than Telerik! Dotnetnuke (DNN) 6.x were awesome releases given they finally replaced VB.NET with C# but sadly they started using Telerik Web UI controls. The Dotnetnuke 6.x is now a maintenance only branch and they never released true .NET4 DNN6 release; due to which; they all have Telerik assemblies compiled for .NET 3.5 and this becomes problematic when your DNN module project is .NET4 and you want to use ACT!
The solution is; either find Telerik Web UI assembly for .NET 4 and compile DNN from source; i-e version ending with something.40 instead of something.35 (for instance DNN 6.2.9 has 2012.2.724.35) or instead of using NUGET for ACT; reference some older version of ACT assembly compiled for .NET3.5 that doesn’t require the TSM and can happily use the Telerik’s RSM that DNN is using!