This is a well stated problem indeed and I believe that it provides most of the relevant information to determine the problem. I say this so that others may learn what qualifies as a good question.
Without having tried out your code, my preliminary analysis suggests that your Register directive is flawed. AFAIK, the Register directive requires at the very least, a tagName, tagPrefix and a src attribute. So, in this case, your Register directive would become something like: --- <%@ Register Namespace="CustomControls" TagPrefix="mycontrol" TagName="WebCustomControl1" Src="~/Usercontrols/WebCustomControl1.ascx "%> --- I suggest you try it out and if it doesn't work, let us know so that we can delve deeper into the problem.
