ldap_search（）操作错误

I've looked at a lot of other questions about this but can't seen to find the solution for my error.

The code I use is:

ldap_set_option(NULL, LDAP_OPT_DEBUG_LEVEL, 7);
$ldapconn = ldap_connect('[HOST]', 389);
ldap_set_option($ldapconn, LDAP_OPT_PROTOCOL_VERSION, 3);
ldap_set_option($ldapconn, LDAP_OPT_REFERRALS, 0);
ldap_bind($ldapconn, $username, $password);

$authUser = $adldap->user()->authenticate($username, $password);
if ($authUser == true) {
    echo "jep";
    echo "<br />";

    $basedn     =   "DC=lab,DC=kuhlmann-its,DC=local";
    $classname  =   "TAI2";
    $filter     =   "(memberOf=OU=" . $classname . ",OU=Accounts,OU=BBS_Students,OU=BBS,OU=EDUNET,DC=lab,DC=kuhlmann-its,DC=local)";
    $attributes =   array("cn");
    $search     =   ldap_search($ldapconn, $basedn, $filter, $attributes);
    $info       =   ldap_get_entries($ldapconn, $search);   

This is my first time working with LDAP and Active Directory and I don't know how all the functions work. I want to know why my ldap_search() is not working.

Thanks in advance.