tabcontainer control giving error 1 could not be set on property 'ActiveTabIndex' and dropdown list control in update panel does not perform any action and gives error in asp.net with c#

Question

hi iam using asp.net with c#
iam using tab ccontainer of ajax control , inside this iam using update panel and drop down list but drop down list not performing any action
and when you select any item from drop down list it gives error
 
error
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Invalid postback or callback argument. Event validation is enabled using <pages enableEventValidation="true"/> in configuration or <%@ Page EnableEventValidation="true" %> in a page. For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them. If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation

and tab container while designing not showing controls and shows 1 could not be set on property 'ActiveTabIndex'