Let me echo what I said to you privately: Thank YOU!!!
The culprit in my case was a malformed DIV tag in the Master Page!!! Never in a million years would I have suspected this!
In my situation, I am developing with VStudio 12 and IE9. I don't use IE10 because it did not work properly with VStudio, at least not when it was first released. But furthermore, my client's corporate standard is IE7 ... yes SEVEN. It's a billion dollar company with tens of thousands of employees around the world so I have no power to require them to upgrade to a modern browser.
Let me describe my page arrangement so you can appreciate how incredible it was that Marin found the problem. In my ASP.NET 4.0 project, I was trying to add RadToolTips to User Controls here:
Parent User Control
Child User Control 1 (CUC1)
Child User Control 2 (CUC2)
I was trying to add RadToolTips to each of the two child user controls. In the attached screenshot, CUC1 are the coloured rectangles you see. CUC2 are the connecting lines. Because the user has to enter a lot of information for each CUC1 they add, I thought it would be useful to display more data in a RadToolTip when they hovered over one of the user controls.
But the RadToolTip failed to display anything! Marin's [super diligent] investigation revealed two causes:
- That I was using IE7 (well, IE9 in IE7 mode).
- That there was a malformed DIV tag in the Master Page.
Further to #2, I had originally had this simple tag in place:
This had been there for years and so I had not looked at it in a long time. But Marin pointed out to me that with the DIV tag, a formal closing tag needs to be present, like this:
After making this change, the RadToolTip suddenly worked in the child user controls!!!
I VERY MUCH appreciate the superb and rapid help provided by Telerik Support! This makes my annual subscription well worth it!!!
Thank you again, Marin.