The GridView 'gvManageProducts' fired event RowDeleting which wasn't handled.

To solve this exception do these:-

protected void gvManageProducts_RowDeleting(object sender, GridViewDeleteEventArgs e)
{
//required -do not remove
}

and also write this:-

protected void gvManageProducts_SelectedIndexChanged(object sender, EventArgs e)
{
//required -do not remove
}