diff --git a/lam/lib/modules/dhcp_settings.inc b/lam/lib/modules/dhcp_settings.inc
index 825ea3c1..d2aca48d 100644
--- a/lam/lib/modules/dhcp_settings.inc
+++ b/lam/lib/modules/dhcp_settings.inc
@@ -366,7 +366,7 @@ By default, the nodes are configured as H-Nodes which fits for small networks. I
 			    $errors[] = $this->messages['cn'][0];
 			}
 			// Check, if cn is not already use:
-		    elseif ( $_SESSION['cache']->in_cache($_POST['cn'],'cn', array('dhcp')) && $this->orig['cn']['0']!=$_POST['cn'] ) {
+		    elseif ((sizeof(searchLDAPByAttribute('cn', $_POST['cn'], 'dhcpOptions', array('cn'), array('dhcp'))) > 0) && $this->orig['cn']['0']!=$_POST['cn']) {
 		       	$errors[] = $this->messages['cn'][1];
 		    }
 			elseif (!check_ip($_POST['cn'],true)) {
diff --git a/lam/lib/modules/sambaGroupMapping.inc b/lam/lib/modules/sambaGroupMapping.inc
index 701d13b2..34177ac4 100644
--- a/lam/lib/modules/sambaGroupMapping.inc
+++ b/lam/lib/modules/sambaGroupMapping.inc
@@ -492,7 +492,8 @@ class sambaGroupMapping extends baseModule {
 				$this->attributes['sambaSID'][0] = $SID."-".$this->rids[$rids[$i]];
 				// Do a check if special group is unique
 				if ($this->getAccountContainer()->isNewAccount) {
-					if ($_SESSION['cache']->in_cache($SID."-".$this->rids[$rids[$i]], 'sambaSID', 'group')) {
+					$result = searchLDAPByAttribute('sambaSID', $SID."-".$this->rids[$rids[$i]], 'sambaGroupMapping', array('sambaSID'), array('group'));
+					if (sizeof($result) > 0) {
 						$message = $this->messages['sambaSID'][0];
 						$message[] = $rids[$i];
 						$errors[] = $message;