How to make a LinkButton in GridView within UpdatePanel do Full PostBack

HI,

i need a solution for this,

i had a gridview, inside that i had a download imagebutton, on clicking this button i need to download the file.

and this gridview is inside update panel. i think trigger to be used but i used both postbacktrigger and asynchronus postback trigger. but it is not triggering the button instead it is giving error.