I faced the same problem, when installing bbpress 1 alpha with integration options (wp2.6) .
The problem is because of automatic generated codes by wordpress api. I installed wp 2.6 and get those codes through api. I had bb-login.php problems when I installed bbpress 1 alpha. And I changed wp codes written in wp-config.php to simple ones( I removed some special characters such a ),”,],/,,[,},{ ) , and then it worked.
I hope this helps you too.
