This could be an .htaccess issue. Could you please post the entire "RewriteRule" area in your forum's .htaccess file, whether the rules are from VaultWiki or not. If you have multiple files in your site's (like 1 file in the root and 1 in the forum directory) please post the requested parts from each relevant file.
As for the "Book" problem, what version of VaultWiki were you running before the upgrade that messed this up?