This isn't really off-topic from my last post but I'll leave it at that for now...
I upgraded my Atlas Control Toolkit to the latest version and all of a sudden, I can no longer link a TextBoxWatermarkExtender and AutoCompleteExtender to the same textbox. I get a message: "Assertion Failed: Duplicate use of id..." etc, etc, and so on and so forth.
In a rare show of common sense, I installed the latest toolkit without removing the previous one so I switched back to the old one and verified that it does in fact work on that version. The problem occurs only in the current (July, I think) CTP of the toolkit. They are aware of the problem so my solution will be to sit and wait.
Stay with me here. This is all going some place.