ldapadd in php not allow more than one variable

I try to add user by using php. ldap_add($ds, "cn=$username, c=$country, dc=graduate, dc=com" , $info); because I want to receive data from my html page. it doesn't work when I try to add more than one variable. But when I try ldap_add($ds, "cn=$username, dc=graduate, dc=com" , $info); or ldap_add($ds, "cn=$username, c=US, dc=graduate, dc=com", $info); it is work. Why? Do you have any solution for this problem

           thank you
           sayumporn

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