I tried out the new 2.0.0beta of the Forum module and I got these 2 errors when viewing a post:
Notice: Undefined index: showPost in /var/www/silverstripe/forum/code/Forum.php on line 401
Notice: Undefined index: start in /var/www/silverstripe/forum/code/Forum.php on line 409
This patch fixes those errors:
http://www.elijahlofgren.com/silverstripe/patches/modules/forum/Fix-undefined-showPost-start-errors-forum-2.0.0beta.patch
Hope this helps,
Elijah