未触发GridView ASP.NET的OnPageIndexChanging事件

I use Stack Overflow all the time for help but I have never had to post my own question on this site. I am also somewhat new to working with ASP.NET web applications. I have a GridView that displays records from a datasource and allows paging to view different pages of the grid. The grid loads fine and displays the data correctly. The problem I am having is that when clicking on a page number nothing happens and my breakpoints are not triggered for Page_Load or OnPageIndexChanging. On MSDN, it says that the OnPageIndexChanging event will fire when selecting a page number on the grid but this is not happening. I have tried all the regularly suggested fixes I have found online for this problem but the issue still persists. I have posted my code below. Can anyone tell me what might cause this event to not get triggered? THANKS IN ADVANCE!I use Stack Overflow all the time for help but