Index: modules/node.module
===================================================================
--- modules/node.module	(revision 19)
+++ modules/node.module	(revision 20)
@@ -1076,7 +1077,12 @@
     $node = node_load(array('nid' => $nid));
 
     unset($node->revisions[$revision]);

+    // if the array is empty, replace the array by an empty string.
+    // otherwise an sql warning will be showed!  
+    if(count($node->revisions)>=0){
+    	$node->revisions='';
+    }
     node_save($node, array('nid', 'revisions'));
 
     drupal_set_message(t('Deleted revision %revision of %title', array('%revision' => "<em>#$revision</em>", '%title' => theme('placeholder', $node->title))));
{