I found the answer in the FAQ — spurious characters added at the end of the file by Expression Web. Solved by saving in Notepad after deleting junk after closing PHP tag.
Solving the “headers already sent” problem
@thebrettman: Hi, added your code to my custom functions.php and received the following error message when logging in to the dashboard:
Warning: Cannot modify header information - headers already sent by (output started at /home/redmon6/public_html/test/wp-content/themes/twentyeleven-child/functions.php:8) in /home/redmon6/public_html/test/wp-includes/pluggable.php on line 866
