Is the wiki node called "Wiki" actually the wiki index? If so, then the URL should not contain a title= parameter (advanced format: /wiki/ is correct, /wiki/Wiki is incorrect)
However if there is a separate page called "Wiki", then it depends if URLs were generated last before Beta 5 build 006 was installed. If this is the case, and the wiki index is inaccessible, then you may need our staff to manually rebuild the wiki path entries in your database.
Please let me know.