Hmm, that looks like its saying that php has not been compiled with the --with-mhash option.
What does it say if you do a phpinfo() ?
Somewhere near the top of the output should be configure information like this:
Configure Command
'./configure' '--with-apxs=/usr/local/apache/bin/apxs' '--with-xml' '--enable-bcmath' '--enable-calendar' '--with-curl' '--enable-ftp' '--with-gd=../gd-1.8.4' '--with-jpeg-dir=/usr/local' '--with-png-dir=/usr' '--with-imap' '--with-kerberos' '--with-mcrypt' '--with-ming=../ming-0.2a' '--enable-magic-quotes' '--with-mysql' '--with-pear' '--enable-safe-mode' '--enable-sockets' '--enable-track-vars' '--with-ttf' '--enable-versioning' '--with-zlib'
I 'think' that yours should include --with-mhash or something like that if it is configured.
Actually, a simpler way would probably be just to put this code in a file:
print_r (get_loaded_extensions());
and see if mhash is included.
see [man]get_loaded_extensions/man for more info.
hope this helps,
Sam