In my web application I'm having a drop down list and a text box. I want to disable the text box for certain values in drop down list. I wrote the code for the selectedIndexChanged event of the drop down list. I made the AutoPostBack property of the drop down list true.

But when I'm running the application and selecting a value from the drop down it suddenly change to the initial value. Therefore all the time I get the value 0 for the SelectedIndex. What can I do for this?