First Google result so i'll add one for "if(!Page.IsPostBack)" in codebehind. I had a repeater with a databound imagebutton. When the button is clicked it threw that error. I finally realized that was trying to rebind my datasource on every postback. It's amazing what staring at your code for 15 minutes can do.

 Not sure if this helps but I just made a break through with this error after quite literally trawling the web for answers.

On my page I had 3 gridviews displaying different information, on one grid I wanted a link to post another page using postbackurl which carried the form values across.

 It turned out that turning off the view state on the other grids allowed the postback to function.

 Hope this helps anyone.

 IIS7 / .NET 2 / VS2008

 

Hey AmirPalang U Trick Worked Thanks Man U Rock :D

AmirPalang: This works!  Thanks so much!

I changed my button type in grid from "Button" to "LinkButton".

this is the correct answer , for the past two days i was struggle to get the output , this post helps me to get the output , thank a lot