I set a reference to AjaxControlToolkit.dll and this added all of the toolkit's controls to my toolbar. I then tried to drag and drop one of the controls to my webform and nothing happened-no error message, no control added to the form. Double clicking the control also did nothing.
The web site compiles with no errors, I also tried to bounce VS2008. I am running Developers Edition on Windows Server 2008.
I was able to add a Script Manager control
This worked w/o issue on my other computers.