I have had similiar errors whilst installing modules with SMF forums.

Warning: Cannot modify header information - headers already sent by (output started at /home/blah/public_html/inc/classes/BxDolGroups.php:419) in /home/blah/public_html/inc/design.inc.php on line 495

It may be that you have installed twice. May i suggest looking in home/blah/public_html/inc/design.inc.php on line 495 and having a look elsewhere in the file to see if the same code has been replicated!

Hope that helps see more you a little!

Mickey