I've got the same problem. I just want to implement an usercontrol into every post.
I used above code and get following Error:
ERROR - UNABLE TO LOAD CONTROL : ~/User controls/Test.ascx
The following code demonstrate what I did.
private static string AppendBody(string Body)
string hBody = Body;
StringBuilder sBuild = new StringBuilder();
hBody = hBody + sBuild.ToString();
The Test.ascx is a very new Control just created with VS 2014 and without any changes.
Best Regards Jürgen