I tried to install the VaultWiki beta last night (shame on me), the install failed at step 4 ... problem is the homepage for our site no longer works. Functionality works if you hit any sub-url or page or forum listing, but just not the homepage...
In case someone else finds this thread looking for a solution:
The OP used another Add-On "AddOn Install & Upgrade" to attempt installing VaultWiki. Due to a bug in AddOn Install & Upgrade at the OP's time of posting, it unzipped VaultWiki files to the wrong locations (including placing a 0-byte index.html file in the forum's home directory).
If an add-on recommends a specific install procedure, it's best to follow those instructions rather than trying to take a shortcut.