jQuery Grid Plugin - jqGrid

I am a newbie to jQuery and your grid.  I am trying to get "MyFirstGrid" running, but I am getting the message "

Cannot modify header information - headers already sent by . . .", 
which refers to the line in example.php "
header("Content-type: text/xml;charset=utf-8");
All I get from the grid is the title, column headers, and the "page 0 of 10" boxes at the bottom.

Where have I gone wrong ?

Thanks.