Looks like your host may of restricted access to certain PHP functions.
Mainly chdir() and unlink().
Or this...
http://uk3.php.net/function.chdir wrote:Note: When safe mode is enabled, PHP checks whether the directory in which the script is operating has the same UID (owner) as the script that is being executed.
Although in most cases the UID is the same if it's in your area of access given by your web host.