[@ipstenu Moderator 15 years, 11 months ago]

In WordPress that error is almost always caused by spaces or blank extra lines in your config file.

http://www.hongkiat.com/blog/wordpress-error-warning-cannot-modify-header-information/

The same is, generally, true of bbPress. Please read the link above to make sure that when we talk about spaces, we’re both talking about the same thing