I just upgraded the files from 1.17.0 to 1.18.0 and after doing so:
Fatal error: Cannot redeclare wfprofilein() (previously declared in /homepages/2/d276811108/htdocs/w/includes/profiler/Profiler.php:14) in /homepages/2/d276811108/htdocs/w/includes/Profiler.php on line 19
I tried the upgrade on my test install it worked fine. I have no idea what is wrong.
Also PHP is version 5.2.17 (cgi)and MySQL is version 5.0.91-log.