Catch errors during bunch encoding

src/app/code/community/AvS/FastSimpleImport/Model/Resource/Import/Data.php

@@ -0,0 +1,35 @@
+<?php
+
+/**
+ * ImportExport import data resource model
+ *
+ * @category   AvS
+ * @package    AvS_FastSimpleImport
+ * @author     Aoe Magento Team <team-magento@aoe.com>
+ * @license    http://opensource.org/licenses/osl-3.0.php Open Software Licence 3.0 (OSL-3.0)
+ * @link       https://github.com/AOEpeople/AvS_FastSimpleImport
+ */
+class AvS_FastSimpleImport_Model_Resource_Import_Data extends Mage_ImportExport_Model_Resource_Import_Data {
+
+    /**
+     * Save import rows bunch.
+     *
+     * @param string $entity
+     * @param string $behavior
+     * @param array $data
+     * @return int
+     * @throws Exception
+     */
+    public function saveBunch($entity, $behavior, array $data)
+    {
+        $json = Mage::helper('core')->jsonEncode($data);
+        if (false === $json) {
+            $error = json_last_error_msg();
+            throw new Exception(sprintf('Error encoding data for save: %s', $error));
+        }
+        return $this->_getWriteAdapter()->insert(
+            $this->getMainTable(),
+            array('behavior' => $behavior, 'entity' => $entity, 'data' => $json)
+        );
+    }
+}

src/app/code/community/AvS/FastSimpleImport/etc/config.xml

@@ -24,6 +24,11 @@
                     <import_entity_product>AvS_FastSimpleImport_Model_Import_Entity_Product</import_entity_product>
                 </rewrite>
             </importexport>
+            <importexport_resource>
+                <rewrite>
+                    <import_data>AvS_FastSimpleImport_Model_Resource_Import_Data</import_data>
+                </rewrite>
+            </importexport_resource>
         </models>
 
         <helpers>