? book.revision-log.patch
? sites/default/files
? sites/default/settings.php
Index: modules/book/book.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/book/book.module,v
retrieving revision 1.475
diff -u -p -r1.475 book.module
--- modules/book/book.module	16 Nov 2008 19:41:14 -0000	1.475
+++ modules/book/book.module	24 Nov 2008 22:57:09 -0000
@@ -746,6 +746,10 @@ function book_nodeapi_presave(&$node, $t
   // Always save a revision for non-administrators.
   if (!empty($node->book['bid']) && !user_access('administer nodes')) {
     $node->revision = 1;
+    // The database schema requires a log message for every revision.
+    if (!isset($node->log)) {
+      $node->log = '';
+    }
   }
   // Make sure a new node gets a new menu link.
   if (empty($node->nid)) {