I'm trying to use the Ajaxtoolkit's ModalPopup functionality in a project where I am already using radTreeViews but whenever I add a reference to the DLL I get runtime javascript errors such as 0x800a138f - JavaScript runtime error: Unable to set property 'control' of undefined or null reference

I tried using the Radwindow control, but frankly, I dislike it due to how it doesn't get along with ajax postbacks. I just want to use the ModalPopup control. it's simple and effective.

why can I not have a reference to the telerik.web.ui (v4.0.30319) and have it work when I also include the AjaxContolToolkit dll referenced in my project?

Hello Robert,

 
Thank you for contacting us.

We haven't encountered this problem before, so we're not quite sure what might be the reason behind it. Would you please send us an isolated simplified sample solution that reproduces the issue, so that we can investigate it locally ( sending the correct dll's as well ) and be more helpful.

I am looking forward for your reply

Regards,
Plamen
Telerik