diff --git a/htdocs/core/lib/company.lib.php b/htdocs/core/lib/company.lib.php
index 238f069c919..1da9f5faedd 100644
--- a/htdocs/core/lib/company.lib.php
+++ b/htdocs/core/lib/company.lib.php
@@ -52,13 +52,15 @@ function societe_prepare_head(Societe $object)
 
 	if (empty($conf->global->MAIN_SUPPORT_SHARED_CONTACT_BETWEEN_THIRDPARTIES)) {
 		if (empty($conf->global->MAIN_DISABLE_CONTACTS_TAB) && $user->rights->societe->contact->lire) {
+			require_once DOL_DOCUMENT_ROOT.'/core/lib/memory.lib.php';
+
 			//$nbContact = count($object->liste_contact(-1,'internal')) + count($object->liste_contact(-1,'external'));
 			$nbContact = 0;
-			$cachekey = 'thirdparty_countcontact_'.$object->id;
-			require_once DOL_DOCUMENT_ROOT.'/core/lib/memory.lib.php';
+			$cachekey = 'thirdparty_'.$object->id.'_countcontacts';
 			$dataretrieved = dol_getcache($cachekey);
-			if (is_array($dataretrieved) && count($dataretrieved)) {
-				$nbContact = $dataretrieved[$cachekey];
+
+			if (!is_null($dataretrieved)) {
+				$nbContact = $dataretrieved;
 			} else {
 				$sql = "SELECT COUNT(p.rowid) as nb";
 				$sql .= " FROM ".MAIN_DB_PREFIX."socpeople as p";
@@ -68,14 +70,10 @@ function societe_prepare_head(Societe $object)
 					$obj = $db->fetch_object($resql);
 					$nbContact = $obj->nb;
 				}
-				$datatocache = array();
-				$datatocache[$cachekey] = $nbContact;
-				$res_setcache = dol_setcache($cachekey, $datatocache);
-				if ($res_setcache < 0) {
-					$error = 'Failed to set cache for cachekey='.$cachekey.' result='.$res_setcache;
-					dol_syslog($error, LOG_ERR);
-				}
+
+				dol_setcache($cachekey, $nbContact);	// If setting cache fails, this is not a problem, so we do not test result.
 			}
+
 			$head[$h][0] = DOL_URL_ROOT.'/societe/contact.php?socid='.$object->id;
 			$head[$h][1] = $langs->trans('ContactsAddresses');
 			if ($nbContact > 0) {
@@ -273,13 +271,14 @@ function societe_prepare_head(Societe $object)
 	if ($user->socid == 0) {
 		// Notifications
 		if (!empty($conf->notification->enabled)) {
+			require_once DOL_DOCUMENT_ROOT.'/core/lib/memory.lib.php';
+
 			$nbNotif = 0;
 			// Enable caching of thirdrparty count notifications
-			$cachekey = 'thirdparty_countnotif_'.$object->id;
-			require_once DOL_DOCUMENT_ROOT.'/core/lib/memory.lib.php';
+			$cachekey = 'thirdparty_'.$object->id.'_countnotifications';
 			$dataretrieved = dol_getcache($cachekey);
-			if (is_array($dataretrieved) && count($dataretrieved)) {
-				$nbNotif = $dataretrieved[$cachekey];
+			if (!is_null($dataretrieved)) {
+				$nbNotif = $dataretrieved;
 			} else {
 				$sql = "SELECT COUNT(n.rowid) as nb";
 				$sql .= " FROM ".MAIN_DB_PREFIX."notify_def as n";
@@ -291,14 +290,9 @@ function societe_prepare_head(Societe $object)
 				} else {
 					dol_print_error($db);
 				}
-				$datatocache = array();
-				$datatocache[$cachekey] = $nbNotif;
-				$res_setcache = dol_setcache($cachekey, $datatocache);
-				if ($res_setcache < 0) {
-					$error = 'Failed to set cache for cachekey='.$cachekey.' result='.$res_setcache;
-					dol_syslog($error, LOG_ERR);
-				}
+				dol_setcache($cachekey, $nbNotif);		// If setting cache fails, this is not a problem, so we do not test result.
 			}
+
 			$head[$h][0] = DOL_URL_ROOT.'/societe/notify/card.php?socid='.$object->id;
 			$head[$h][1] = $langs->trans("Notifications");
 			if ($nbNotif > 0) {
@@ -343,13 +337,14 @@ function societe_prepare_head(Societe $object)
 	$head[$h][0] = DOL_URL_ROOT.'/societe/agenda.php?socid='.$object->id;
 	$head[$h][1] = $langs->trans("Events");
 	if (!empty($conf->agenda->enabled) && (!empty($user->rights->agenda->myactions->read) || !empty($user->rights->agenda->allactions->read))) {
-		// Enable caching of thirdrparty count actioncomm
-		$nbEvent = 0;
-		$cachekey = 'thirdparty_countevent_'.$object->id;
 		require_once DOL_DOCUMENT_ROOT.'/core/lib/memory.lib.php';
+
+		$nbEvent = 0;
+		// Enable caching of thirdrparty count actioncomm
+		$cachekey = 'thirdparty_'.$object->id.'_countevents';
 		$dataretrieved = dol_getcache($cachekey);
-		if (is_array($dataretrieved) && count($dataretrieved)) {
-			$nbEvent = $dataretrieved[$cachekey];
+		if (!is_null($dataretrieved)) {
+			$nbEvent = $dataretrieved;
 		} else {
 			$sql = "SELECT COUNT(id) as nb";
 			$sql .= " FROM ".MAIN_DB_PREFIX."actioncomm";
@@ -361,14 +356,9 @@ function societe_prepare_head(Societe $object)
 			} else {
 				dol_syslog('Failed to count actioncomm '.$db->lasterror(), LOG_ERR);
 			}
-			$datatocache = array();
-			$datatocache[$cachekey] = $nbEvent;
-			$res_setcache = dol_setcache($cachekey, $datatocache);
-			if ($res_setcache < 0) {
-				$error = 'Failed to set cache for cachekey='.$cachekey.' result='.$res_setcache;
-				dol_syslog($error, LOG_ERR);
-			}
+			dol_setcache($cachekey, $nbEvent);		// If setting cache fails, this is not a problem, so we do not test result.
 		}
+
 		$head[$h][1] .= '/';
 		$head[$h][1] .= $langs->trans("Agenda");
 		if ($nbEvent > 0) {
diff --git a/htdocs/core/lib/memory.lib.php b/htdocs/core/lib/memory.lib.php
index 11fa6082b05..818ff0bf171 100644
--- a/htdocs/core/lib/memory.lib.php
+++ b/htdocs/core/lib/memory.lib.php
@@ -88,7 +88,7 @@ function dol_setcache($memoryid, $data)
 		} else {
 			return -$rescode;
 		}
-	} elseif (!empty($conf->memcached->enabled) && class_exists('Memcache')) {
+	} elseif (!empty($conf->memcached->enabled) && class_exists('Memcache')) {	// This is a really not reliable cache ! Use Memcached instead.
 		// Using a memcache server
 		global $dolmemcache;
 		if (empty($dolmemcache) || !is_object($dolmemcache)) {
@@ -106,7 +106,7 @@ function dol_setcache($memoryid, $data)
 		} else {
 			return -1;
 		}
-	} elseif (isset($conf->global->MAIN_OPTIMIZE_SPEED) && ($conf->global->MAIN_OPTIMIZE_SPEED & 0x02)) {
+	} elseif (isset($conf->global->MAIN_OPTIMIZE_SPEED) && ($conf->global->MAIN_OPTIMIZE_SPEED & 0x02)) {	// This is a really not reliable cache ! Use Memcached instead.
 		// Using shmop
 		$result = dol_setshmop($memoryid, $data);
 	}
@@ -140,14 +140,16 @@ function dol_getcache($memoryid)
 		//print "Get memoryid=".$memoryid;
 		$data = $m->get($memoryid);
 		$rescode = $m->getResultCode();
-		//print "memoryid=".$memoryid." - rescode=".$rescode." - data=".count($data)."\n<br>";
+		//print "memoryid=".$memoryid." - rescode=".$rescode." - count(response)=".count($data)."\n<br>";
 		//var_dump($data);
 		if ($rescode == 0) {
 			return $data;
+		} elseif ($rescode == 16) {		// = Memcached::MEMCACHED_NOTFOUND but this constant doe snot exists.
+			return null;
 		} else {
 			return -$rescode;
 		}
-	} elseif (!empty($conf->memcached->enabled) && class_exists('Memcache')) {
+	} elseif (!empty($conf->memcached->enabled) && class_exists('Memcache')) {	// This is a really not reliable cache ! Use Memcached instead.
 		global $m;
 		if (empty($m) || !is_object($m)) {
 			$m = new Memcache();
@@ -164,9 +166,9 @@ function dol_getcache($memoryid)
 		if ($data) {
 			return $data;
 		} else {
-			return -1;
+			return null;		// There is no way to make a difference between NOTFOUND and error when using Memcache. So do not use it, use Memcached instead.
 		}
-	} elseif (isset($conf->global->MAIN_OPTIMIZE_SPEED) && ($conf->global->MAIN_OPTIMIZE_SPEED & 0x02)) {
+	} elseif (isset($conf->global->MAIN_OPTIMIZE_SPEED) && ($conf->global->MAIN_OPTIMIZE_SPEED & 0x02)) {	// This is a really not reliable cache ! Use Memcached instead.
 		// Using shmop
 		$data = dol_getshmop($memoryid);
 		return $data;
@@ -186,7 +188,7 @@ function dol_getcache($memoryid)
 function dol_getshmopaddress($memoryid)
 {
 	global $shmkeys, $shmoffset;
-	if (empty($shmkeys[$memoryid])) {
+	if (empty($shmkeys[$memoryid])) {	// No room reserved for thid memoryid, no way to use cache
 		return 0;
 	}
 	return $shmkeys[$memoryid] + $shmoffset;
@@ -215,8 +217,8 @@ function dol_listshmop()
  * 	Save data into a memory area shared by all users, all sessions on server
  *
  *  @param	int		$memoryid		Memory id of shared area ('main', 'agenda', ...)
- * 	@param	string	$data			Data to save
- * 	@return	int						<0 if KO, Nb of bytes written if OK
+ * 	@param	string	$data			Data to save. Must be a not null value.
+ * 	@return	int						<0 if KO, 0=Caching not available, Nb of bytes written if OK
  */
 function dol_setshmop($memoryid, $data)
 {
@@ -225,6 +227,8 @@ function dol_setshmop($memoryid, $data)
 	//print 'dol_setshmop memoryid='.$memoryid."<br>\n";
 	if (empty($shmkeys[$memoryid]) || !function_exists("shmop_write")) return 0;
 	$shmkey = dol_getshmopaddress($memoryid);
+	if (empty($shmkey)) return 0;	// No key reserved for this memoryid, we can't cache this memoryid
+
 	$newdata = serialize($data);
 	$size = strlen($newdata);
 	//print 'dol_setshmop memoryid='.$memoryid." shmkey=".$shmkey." newdata=".$size."bytes<br>\n";
@@ -247,14 +251,20 @@ function dol_setshmop($memoryid, $data)
  * 	Read a memory area shared by all users, all sessions on server
  *
  *  @param	string	$memoryid		Memory id of shared area ('main', 'agenda', ...)
- * 	@return	int						<0 if KO, data if OK
+ * 	@return	int						<0 if KO, data if OK, Null if no cache enabled or not found
  */
 function dol_getshmop($memoryid)
 {
 	global $shmkeys, $shmoffset;
 
-	if (empty($shmkeys[$memoryid]) || !function_exists("shmop_open")) return 0;
+	$data = null;
+
+	if (empty($shmkeys[$memoryid]) || !function_exists("shmop_open")) {
+		return null;
+	}
 	$shmkey = dol_getshmopaddress($memoryid);
+	if (empty($shmkey)) return null;		// No key reserved for this memoryid, we can't cache this memoryid
+
 	//print 'dol_getshmop memoryid='.$memoryid." shmkey=".$shmkey."<br>\n";
 	$handle = @shmop_open($shmkey, 'a', 0, 0);
 	if ($handle) {
@@ -263,7 +273,7 @@ function dol_getshmop($memoryid)
 		else return -1;
 		shmop_close($handle);
 	} else {
-		return -2;
+		return null;	// Can't open existing block, so we suppose it was not created, so nothing were cached yet for the memoryid
 	}
 	return $data;
 }