How to update custom controls in toolbox

I have added a custom control to the toolbox and it worked fine until I rebuilt the control and tried to update it in the toolbox.  now whenever I try to drag the control onto an ASCX page it does nothing.  I tried removing all references to the control in the ASCX file and in the project references and from the toolbox itself.  But no matter what I do my control simply does nothing when it is dragged from the toolbox onto the ASCX page.  Am I missing something?  Can anyone help.