Re: HomePage 404 - File or directory not found
If /tiki-index.php?page=HomePage works, and /HomePage gives you a 404, you probably selected the "Search engine friendly URL" feature, and did not set up the .htaccess file correctly. If you cannot get the .htaccess to rewrite the /HomePage URL, unselect the "Search engine friendly URL" feature through Admin, Features, Global features tab.
See: http://doc.tiki.org/Search+Engine+Friendly+URL
There is a note near the bottom: "Do not use this feature when installing Tiki on IIS server".