When I load my wowroster diag, the top of the screen becomes flooded with:

Notice: Undefined offset: 1 in /home/controla/public_html/wowroster/lib/rosterdiag.lib.php on line 260
and
Notice: Undefined offset: 1 in /home/controla/public_html/wowroster/lib/rosterdiag.lib.php on line 260

repeating itself about 10 times, and it ends with :

Warning: Cannot modify header information - headers already sent by (output started at /home/controla/public_html/wowroster/lib/rosterdiag.lib.php:260) in /home/controla/public_html/wowroster/rosterdiag.php on line 51.

In short, should I be worried, and how can i fix these errors.