diff --git a/admin/inc/class.admin_account.inc.php b/admin/inc/class.admin_account.inc.php
index 07cca00308..72da46e171 100644
--- a/admin/inc/class.admin_account.inc.php
+++ b/admin/inc/class.admin_account.inc.php
@@ -331,7 +331,7 @@ class admin_account
 			$msg = '';
 			if(count($content['account_id']) == 1)
 			{
-				self::_deferred_delete($content['account_id'][0], $content['new_owner'], $content['delete_apps'], $content['admin_cmd']);
+				self::_deferred_delete($account_id, $content['new_owner'], $content['delete_apps'], $content['admin_cmd']);
 				if ($content['contact_id'])
 				{
 					Framework::refresh_opener($msg, 'addressbook', $content['contact_id'], 'delete');
@@ -356,7 +356,7 @@ class admin_account
 		// Get a count of entries owned by the user
 		if(count($content['account_id']) == 1)
 		{
-			$_counts = $GLOBALS['egw']->accounts->get_account_entry_counts($content['account_id'][0]);
+			$_counts = $GLOBALS['egw']->accounts->get_account_entry_counts($content['account_id']);
 		}
 		else
 		{
diff --git a/admin/inc/class.admin_config.inc.php b/admin/inc/class.admin_config.inc.php
index f72a54d030..22251689b1 100644
--- a/admin/inc/class.admin_config.inc.php
+++ b/admin/inc/class.admin_config.inc.php
@@ -144,7 +144,13 @@ class admin_config
 				$this->remove_anon_images(array_diff((array)$c->config_data['login_background_file'], (array)$_content['newsettings']['login_background_file']));
 			}
 
-			/* Load hook file with functions to validate each config (one/none/all) */
+			// "config_validate" hook returns a non-empty string with an error-message (everything else is treated as no error)
+			// The hook can additional set $GLOBALS['egw_info']['server']['found_validation_hook'] with individual validation-functions:
+			// a) regular function names matching the config-name or "final_validation" as values or
+			// b) same key as config-value for a callable eg. $GLOBALS['egw_info']['server']['found_validation_hook'][<name>]='<class-name>::<name>'
+			// The validation-function can return a non-empty string with an error (or deprecated set $GLOBALS['config_error']).
+			// Function signature: ?string function(mixed $value, Api\Config $c) ($c can be used to modify the value to save: $c->config_data[$name]=$val)
+			// Please note: only b) can be implemented in the file of a namespaced class
 			$errors = Api\Hooks::single(array(
 				'location' => 'config_validate',
 			)+(array)$_content['newsettings'], $appname);
@@ -155,12 +161,14 @@ class admin_config
 				if ($config)
 				{
 					$c->config_data[$key] = $config;
-					if (in_array($key, (array)$GLOBALS['egw_info']['server']['found_validation_hook'], true) && function_exists($key))
+					if (in_array($key, (array)$GLOBALS['egw_info']['server']['found_validation_hook'], true) &&
+							function_exists($func=$key) ||
+						isset($GLOBALS['egw_info']['server']['found_validation_hook'][$key]) &&
+							is_callable($func=$GLOBALS['egw_info']['server']['found_validation_hook'][$key]))
 					{
-						call_user_func($key, $config, $c);
-						if($GLOBALS['config_error'])
+						if (is_string($err=$func($config, $c)) || ($err=$GLOBALS['config_error']))
 						{
-							$errors .= lang($GLOBALS['config_error']) . "\n";
+							$errors .= lang($err) . "\n";
 							$GLOBALS['config_error'] = False;
 						}
 					}
@@ -171,17 +179,18 @@ class admin_config
 					unset($c->config_data[$key]);
 				}
 			}
-			if(in_array('final_validation', (array)$GLOBALS['egw_info']['server']['found_validation_hook']) &&
-				function_exists('final_validation'))
+			if (in_array('final_validation', (array)$GLOBALS['egw_info']['server']['found_validation_hook']) &&
+					function_exists($func='final_validation') ||
+				isset($GLOBALS['egw_info']['server']['found_validation_hook']['final_validation']) &&
+					is_callable($func=$GLOBALS['egw_info']['server']['found_validation_hook']['final_validation']))
 			{
-				final_validation($_content['newsettings']);
-				if($GLOBALS['config_error'])
+				if (is_string($err=$func($_content['newsettings'])) || ($err=$GLOBALS['config_error']))
 				{
-					$errors .= lang($GLOBALS['config_error']) . "\n";
+					$errors .= lang($err) . "\n";
 					$GLOBALS['config_error'] = False;
 				}
-				unset($GLOBALS['egw_info']['server']['found_validation_hook']);
 			}
+			unset($GLOBALS['egw_info']['server']['found_validation_hook']);
 
 			// do not allow to save config, if there are errors
 			if (!$errors)