grid view SelectedIndexChanged

Question

I have Gridiew1 in page one when click on Auto Generate select Button take you to page tow and fill it's control from selected row using session

as :   TextBox1.Text = Session["cell1"].ToString();

         TextBox2.Text = Session["cell2"].ToString();

it is work fine but when I click the grid page index give this error:

Gridview Fired Event 'Sorting' which wasn't handled

when put Auto Generate select Button to false grid page work without error

thank you all