The most likely reason for such a problem is that AJAX is used and the notification does not participate in the partial rendering in all cases it needs to. Most likely, you have an AJAX setting where grdTenders is an initiator and n1 is an UpdatedControl, so you would need a similar setting where grdTenDetails is the initiator and n1 is updated.
An alternative is to remove the n1 control from such AJAX settings and wrap it in an asp:UpdatePanel with UpdateMode=Conditional. Thus, you can call the update panel's Update() server method when you need to show the notification and be sure that it will travel to the client.
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.