Please, try the solution provided in the following forum thread: RadEditor is not working at all inside a ModalPopupExtender
The other thing to try is to fire the onParentNodeChanged
method of RadEditor when the ModalPopupExtender is shown as shown in these forums:
To fix the background color issue use the solution provided in this help article: Content Area Appearance Problems
If you are unable to solve the problems, isolate them in a simple runnable project and send it for examination via a support ticket.
the Telerik team
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