Go to AdminCP > VaultWiki > Wiki URL Manager, and click [Rebuild Page URLs]. In VaultWiki 3, there was sometimes an issue when moving sub-forums or enabling them for the wiki which caused existing URLs in that forum to go out of sync.
This is discussed in one of my blogs on the subject, but in VaultWiki 4, we will be able to store all this information in one place so there will not be sync issues.