Index: modules/book/book.install
===================================================================
RCS file: /cvs/drupal/drupal/modules/book/book.install,v
retrieving revision 1.20.2.1
diff -u -r1.20.2.1 book.install
--- modules/book/book.install   6 Jan 2009 15:46:36 -0000       1.20.2.1
+++ modules/book/book.install   28 Jan 2009 19:43:24 -0000
@@ -201,8 +201,12 @@
 
       if ($book['parent']) {
         // If its not a top level page, get its parent's mlid.
-        $parent = db_fetch_array(db_query("SELECT b.mlid AS plid, b.bid FROM {book} b WHERE b.nid = %d", $book['parent']));
-        $book = array_merge($book, $parent);
+        if ($parent = db_fetch_array(db_query("SELECT b.mlid AS plid, b.bid FROM {book} b WHERE b.nid = %d", $book['parent']))) {
+          $book = array_merge($book, $parent);
+        }
+        else {
+          watchdog('debug', 'Book anomaly. Entry for parent '. $book['parent'] .' not found in book table.');
+        }
       }
       else {
         // There is not a parent - this is a new book.