CascadingDropDown require EventVlidation=false?

I turned on event validation (=true) of the Atlas Control Toolkit sample -> CascadingDropDown .

When I click the , Error message suggest turn event validation off.

Is this a must?

I saw some thread showing that they can add an attribute "SuppressEventValidation", but I can't see smart tag/ code hints in my version? Is it a new feature in later built of atlas?

Please advice how to keep EventValidated ?

This thread explains why I believe EnableEventValidation needs to be false:http://forums.asp.net/thread/1281139.aspx

Thanks for your kindly reference, It's really a time for me to choose between SECURITY , USABLITILY

I need to sacrifice security , choose usablitiliy