either
(e.Row.FindControl("LL0") as Label)
is returning null or
ddrrpp.Items.FindByValue((e.Row.FindControl("LL0") as Label).Text)
is null. You should be checking for null on both of them before trying to call one of their properties.
Label label = (e.Row.FindControl("LL0") as Label);
if (label != null)
{
ListItem item = ddrrpp.Items.FindByValue((e.Row.FindControl("LL0") as Label).Text);
if (item != null)
{
item.Selected = true;
}
}
This should keep your page from crashing but there's no guarantee that it will operate in the way you think it should. That will depend on how your GridView is set up. However, you should be able to step through this using the debugger and determine which object is null.