Error The GridView fired event PageIndexChanging which wasn't handled

Hi,

I set paging in grid view control but got error when clicked on paging number below the grid.

Error:

The GridView 'Grid_part_stock' fired event PageIndexChanging which wasn't handled.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace: 

[HttpException (0x80004005): The GridView 'Grid_part_stock' fired event PageIndexChanging which wasn't handled.]
   System.Web.UI.WebControls.GridView.OnPageIndexChanging(GridViewPageEventArgs e) +1464505
   System.Web.UI.WebControls.GridView.HandlePage(Int32 newPage) +62
   System.Web.UI.WebControls.GridView.HandleEvent(EventArgs e, Boolean causesValidation, String validationGroup) +408
   System.Web.UI.WebControls.GridView.RaisePostBackEvent(String eventArgument) +210
   System.Web.UI.WebControls.GridView.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +13
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +176
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +5563