can't get memberof filter working

Hi all. Im having hard time triyng to figure out what is wrong with this ldap query:

Im triyng to filter a specific user inside a specific group. Like this /usr/bin/ldapsearch -x -D ".." -w.. -b "o=Work" "(&(uniquemember=uid=gherzig,ou=People,o=Work) (memberof=cn=MailUsers,ou=Groups,o=Work))"

It gets no results, but if i remove the memberof part, it works good. "(&(uniquemember=uid=gherzig,ou=People,o=Work))" as a filter gives me all the entries that users is in.

What is wrong? BTW specifiyng a different basesearch is not an option, i need that base as it is.

Thanks!! Gerardo