Missing argument 2

Yes, it's the bug. Here's the quick solution:

--- ajaxblocks.module.orig      2011-03-28 03:37:11.000000000 +0400
+++ ajaxblocks.module   2011-03-31 12:13:07.667524051 +0400
@@ -27,7 +27,8 @@
 function ajaxblocks_form_block_admin_configure_alter(&$form, &$form_state) {
   // Retrieve current setting for this block.
   $block_id = $form['module']['#value'] . '-' .  $form['delta']['#value'];
-  $value = (int) ajaxblocks_is_ajax($block_id);
+  $loader_picture = 0;
+  $value = (int) ajaxblocks_is_ajax($block_id, $loader_picture);

   $options = array(0 => t('no'), 1 => t('yes'));

@@ -60,7 +61,7 @@
     '#title' => t('Loader picture'),
     '#description' => t('Choose the background picture for the block for AJAX loadding period.'),
     '#options' => $pictures,
-    '#default_value' => intval(db_result(db_query("SELECT loader_picture FROM {ajaxblock} WHERE block_id = '%s'", $block_id))),
+    '#default_value' => $loader_picture,
   );

   $form['submit']['#weight'] = 2;

hi i put the fix on, but it solved not the issue for me..i get the error msg in the block config

The issue is fixed in 6.x-1.4 release.