In addition, you might get this wierd error message on the top of phpWiki on the first visit to a page (it disappears after a refresh):
>lib/Request.php:136: Warning[2]: ob_start(): output handler
'ob_gzhandler' cannot be used after 'URL-Rewriter'
The solution to this can be found Here or just keep reading.
1. Find your index.php file in the phpwiki directory
2. Find the line that states:
>define('COMPRESS_OUTPUT', false);
3. Un comment the line, or make sure that the setting is indeed false.
That should do it, the explanation off the website linked above is: