In order to develop with the Engine controls, you need an Engine developer license. This didn't use to be the case but it changed a few versions back. We have several applications that were originally built back in 8.x that use the MapControl and we continue to use it without any problems, upgrading/recompiling the code with each new version. Each time I open a form that has the control, I get a message stating I need the Engine dev license. I dismiss the message and can edit the code behind the form as well as add/remove standard form controls. I'm not sure if I can actually edit the MapControl though as I've never had the need. That being said, if you're trying to add the control to a form then I would imagine you need the license.