vbSEO Forum Conflict
When vbSEO is set to interpret forum URLs in the format "/[forum_title]/" - that is, with no static forum URL identifier like "/forum-[forum_title]/", it interprets Simple Wiki URLs as invalid forum URLs. An error message that the forum is invalid is displayed rather than the wiki page.
This can be fixed by modifying vbSEO's RewriteRules, but there must be some other workaround.