In your AdminCP, go to vBulletin CMS, and click "Clear CMS Cache". This happens when you disable/re-enable VaultWiki (or any product with content-types) using the [APM] Advanced Product Manager modification, but content types were purged while VaultWiki was disabled (like if it was disabled during a vBulletin upgrade). That modification (APM) doesn't have support for vB_Cache, so the content types are not rebuilt when you re-enable a product.
I reported this issue to the mod creator months ago, but my guess is they still haven't fixed it. The only workaround for now is to make sure you do all your enabling/disabling through vB's default Product Manager.