fixed error (object to string conversion), better message

Author: sreichel

app/code/core/Mage/Core/Model/Layout.php

@@ -503,12 +503,12 @@ protected function _getBlockInstance($block, array $attributes = [])
                 }
             }
             if (class_exists($block, false) || mageFindClassFile($block)) {
-                // phpcs:ignore Ecg.Classes.ObjectInstantiation.DirectInstantiation
                 $block = new $block($attributes);
             }
         }
         if (!$block instanceof Mage_Core_Block_Abstract) {
-            Mage::throwException(Mage::helper('core')->__('Invalid block type: %s', $block));
+            $block = is_object($block) ? get_class($block) : $block;
+            Mage::throwException(Mage::helper('core')->__('Invalid block type: %s (not instance of Mage_Core_Block_Abstract)', $block));
         }
         return $block;
     }

app/locale/en_US/Mage_Core.csv

@@ -175,6 +175,7 @@
 "Invalid URL scheme.","Invalid URL scheme."
 "Invalid base url type","Invalid base url type"
 "Invalid block type: %s","Invalid block type: %s"
+"Invalid block type: %s (not instance of Mage_Core_Block_Abstract)","Invalid block type: %s (not instance of Mage_Core_Block_Abstract)"
 "Invalid block: %s","Invalid block: %s"
 "Invalid connection","Invalid connection"
 "Invalid date","Invalid date"