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#

for your second problem of ActiveTabIndex

you should go through my article on Enhancing the functionality of Ajax Tab Control

it'll surely help you

Please Don't forget to mark "Do you like this post" if it helps.

hi friend,

there is two solution for this problem.

1. set EnableEventValidation="false" attribute of aspx <%@page--%> tag .

2. Or if you have some code written inside the page_load event if not necessary to call the code at postback then

  if(!Page.IsPostBack)
{
   // you complete code inside page_load event will go here
}

Any of the above method will solve your problem.. but choose second one carefully it may change your behavior of program while postback.

Please Don't forget to mark "Do you like this post" if it helps.