diff --git a/Project/php/model/UserGateway.php b/Project/php/model/UserGateway.php
index 3f22e37..6c1f0a1 100755
--- a/Project/php/model/UserGateway.php
+++ b/Project/php/model/UserGateway.php
@@ -17,98 +17,145 @@ class UserGateway
     }
 
     public function findAllUsers() : array{
-        $query = "SELECT * FROM User_";
-        $this->con->executeQuery($query, array());
-        $results = $this->con->getResults();
-        $tab = array();
-        foreach ($results as $row)
-            $tab[] = new User($row['id'], $row['password'], $row['email'], $row['name'], $row['surname'], $row['nickname'], $row['image'], $row['extraTime'], $row['groupID']);
-        return $tab;
+        try {
+            $query = "SELECT * FROM User_";
+            $this->con->executeQuery($query, array());
+            $results = $this->con->getResults();
+            $tab = array();
+            foreach ($results as $row)
+                $tab[] = new User($row['id'], $row['password'], $row['email'], $row['name'], $row['surname'], $row['nickname'], $row['image'], $row['extraTime'], $row['groupID']);
+            return $tab;
+        }
+        catch(PDOException $e ){
+            error_log('PDOException: ' . $e->getMessage(), 3, 'error.log');
+            return array();
+        }
     }
 
     public function findUserById(int $id) : array{
-        $query = "SELECT * FROM User_ WHERE id=:id";
-        $args = array(':id' => array($id, PDO::PARAM_INT));
-        $this->con->executeQuery($query, $args);
-        $results = $this->con->getResults();
-        $tab = array();
-        foreach ($results as $row)
-            $tab[] = new User($row['id'], $row['password'], $row['email'], $row['name'], $row['surname'], $row['nickname'], $row['image'], $row['extraTime'], $row['groupID']);
-        return $tab;
+        try {
+            $query = "SELECT * FROM User_ WHERE id=:id";
+            $args = array(':id' => array($id, PDO::PARAM_INT));
+            $this->con->executeQuery($query, $args);
+            $results = $this->con->getResults();
+            $tab = array();
+            foreach ($results as $row)
+                $tab[] = new User($row['id'], $row['password'], $row['email'], $row['name'], $row['surname'], $row['nickname'], $row['image'], $row['extraTime'], $row['groupID']);
+            return $tab;
+        }
+        catch(PDOException $e ){
+            error_log('PDOException: ' . $e->getMessage(), 3, 'error.log');
+            return array();
+        }
     }
 
     public function findUserByName(string $name) : array{
-        $query = "SELECT * FROM User_ WHERE name=:name";
-        $args = array(':name' => array($name, PDO::PARAM_STR));
-        $this->con->executeQuery($query, $args);
-        $results = $this->con->getResults();
-        $tab = array();
-        foreach ($results as $row)
-            $tab[] = new User($row['id'], $row['password'], $row['email'], $row['name'], $row['surname'], $row['nickname'], $row['image'], $row['extraTime'], $row['groupID']);
-        return $tab;
+        try {
+            $query = "SELECT * FROM User_ WHERE name=:name";
+            $args = array(':name' => array($name, PDO::PARAM_STR));
+            $this->con->executeQuery($query, $args);
+            $results = $this->con->getResults();
+            $tab = array();
+            foreach ($results as $row)
+                $tab[] = new User($row['id'], $row['password'], $row['email'], $row['name'], $row['surname'], $row['nickname'], $row['image'], $row['extraTime'], $row['groupID']);
+            return $tab;
+        }
+        catch(PDOException $e ){
+            error_log('PDOException: ' . $e->getMessage(), 3, 'error.log');
+            return array();
+        }
     }
 
     public function findUserBySurname(string $surname) : array{
-        $query = "SELECT * FROM User_ WHERE surname=:surname";
-        $args = array(':surname' => array($surname, PDO::PARAM_STR));
-        $this->con->executeQuery($query, $args);
-        $results = $this->con->getResults();
-        $tab = array();
-        foreach ($results as $row)
-            $tab[] = new User($row['id'], $row['password'], $row['email'], $row['name'], $row['surname'], $row['nickname'], $row['image'], $row['extraTime'], $row['groupID']);
-        return $tab;
+        try {
+            $query = "SELECT * FROM User_ WHERE surname=:surname";
+            $args = array(':surname' => array($surname, PDO::PARAM_STR));
+            $this->con->executeQuery($query, $args);
+            $results = $this->con->getResults();
+            $tab = array();
+            foreach ($results as $row)
+                $tab[] = new User($row['id'], $row['password'], $row['email'], $row['name'], $row['surname'], $row['nickname'], $row['image'], $row['extraTime'], $row['groupID']);
+            return $tab;
+        }
+        catch(PDOException $e ){
+            error_log('PDOException: ' . $e->getMessage(), 3, 'error.log');
+            return array();
+        }
     }
 
     public function findUserByNickname(string $nickname) : array{
-        $query = "SELECT * FROM User_ WHERE nickname=:nickname";
-        $args = array(':nickname' => array($nickname, PDO::PARAM_STR));
-        $this->con->executeQuery($query, $args);
-        $results = $this->con->getResults();
-        $tab = array();
-        foreach ($results as $row)
-            $tab[] = new User($row['id'], $row['password'], $row['email'], $row['name'], $row['surname'], $row['nickname'], $row['image'], $row['extraTime'], $row['groupID']);
-        return $tab;
+        try {
+            $query = "SELECT * FROM User_ WHERE nickname=:nickname";
+            $args = array(':nickname' => array($nickname, PDO::PARAM_STR));
+            $this->con->executeQuery($query, $args);
+            $results = $this->con->getResults();
+            $tab = array();
+            foreach ($results as $row)
+                $tab[] = new User($row['id'], $row['password'], $row['email'], $row['name'], $row['surname'], $row['nickname'], $row['image'], $row['extraTime'], $row['groupID']);
+            return $tab;
+        }
+        catch(PDOException $e ){
+            error_log('PDOException: ' . $e->getMessage(), 3, 'error.log');
+            return array();
+        }
     }
 
-    public function isAdmin(int $id):bool {
-        $query = "SELECT * FROM Be WHERE userID=:id AND roleID=1";
-        $args = array(':id' => array($id, PDO::PARAM_INT));
-        $this->con->executeQuery($query, $args);
-        return !empty($this->con->getResults());
+    public function isAdmin(int $id) : bool {
+        try {
+            $query = "SELECT * FROM Be WHERE userID=:id AND roleID=1";
+            $args = array(':id' => array($id, PDO::PARAM_INT));
+            $this->con->executeQuery($query, $args);
+            return !empty($this->con->getResults());
+        }
+        catch(PDOException $e ){
+            error_log('PDOException: ' . $e->getMessage(), 3, 'error.log');
+            return false;
+        }
     }
 
     public function addUser(string $password, string $email, string $name, string $surname, string $nickname, string $image, bool $extraTime, int $group, array $roles): int {
-        $query = "INSERT INTO User_ VALUES (NULL, :password, :email, :name, :surname, :nickname, :image, :extraTime, :group)";
-        $args = array(':password' => array($password, PDO::PARAM_STR),
-            ':email' => array($email, PDO::PARAM_STR),
-            ':name' => array($name, PDO::PARAM_STR),
-            ':surname' => array($surname, PDO::PARAM_STR),
-            ':nickname' => array($nickname, PDO::PARAM_STR),
-            ':image' => array($image, PDO::PARAM_STR),
-            ':extraTime' => array($extraTime, PDO::PARAM_BOOL),
-            ':group' => array($group, PDO::PARAM_INT));
-        $this->con->executeQuery($query, $args);
-        $userID = $this->con->lastInsertId();
-
-        foreach ($roles as $role) {
-            $query = "INSERT INTO Be VALUES (:userID, :roleID)";
-            $args = array(':userID' => array($userID, PDO::PARAM_INT),
-                ':roleID' => array($role, PDO::PARAM_INT));
+        try {
+            $query = "INSERT INTO User_ VALUES (NULL, :password, :email, :name, :surname, :nickname, :image, :extraTime, :group)";
+            $args = array(':password' => array($password, PDO::PARAM_STR),
+                ':email' => array($email, PDO::PARAM_STR),
+                ':name' => array($name, PDO::PARAM_STR),
+                ':surname' => array($surname, PDO::PARAM_STR),
+                ':nickname' => array($nickname, PDO::PARAM_STR),
+                ':image' => array($image, PDO::PARAM_STR),
+                ':extraTime' => array($extraTime, PDO::PARAM_BOOL),
+                ':group' => array($group, PDO::PARAM_INT));
             $this->con->executeQuery($query, $args);
-        }
+            $userID = $this->con->lastInsertId();
+
+            foreach ($roles as $role) {
+                $query = "INSERT INTO Be VALUES (:userID, :roleID)";
+                $args = array(':userID' => array($userID, PDO::PARAM_INT),
+                    ':roleID' => array($role, PDO::PARAM_INT));
+                $this->con->executeQuery($query, $args);
+            }
 
-        return $userID;
+            return $userID;
+        }
+        catch(PDOException $e ){
+            error_log('PDOException: ' . $e->getMessage(), 3, 'error.log');
+            return 0;
+        }
     }
 
     public function RemoveUser(int $id) {
-        $query="DELETE FROM Vocabulary WHERE creator=:id";
-        $args = array(':id' => array($id, PDO::PARAM_INT));
-        $this->con->executeQuery($query, $args);
+        try {
+            $query="DELETE FROM Vocabulary WHERE creator=:id";
+            $args = array(':id' => array($id, PDO::PARAM_INT));
+            $this->con->executeQuery($query, $args);
 
-        $query="DELETE FROM Be WHERE userID=:id";
-        $this->con->executeQuery($query, $args);
+            $query="DELETE FROM Be WHERE userID=:id";
+            $this->con->executeQuery($query, $args);
 
-        $query="DELETE FROM User_ WHERE id=:id";
-        $this->con->executeQuery($query, $args);
+            $query="DELETE FROM User_ WHERE id=:id";
+            $this->con->executeQuery($query, $args);
+        }
+        catch(PDOException $e ){
+                error_log('PDOException: ' . $e->getMessage(), 3, 'error.log');
+        }
     }
 }
\ No newline at end of file