Hi! tedsmith
It's nothing.

1. Sorry, I have made a mistake. the file name of mine is also notification.inc.php not notification.php.
2. I mean make sure the things in the second quote (here is E:/Www/xoops) in the following line in mainfile.php to be lowercase
define('XOOPS_ROOT_PATH', 'E:/Www/xoops');

So for better, this line after modified should be like :
define('XOOPS_ROOT_PATH', 'e:/www/xoops');

By the way!
The problem is caused by php's include_once() function and this function's case sensitive attribute. So when your host is based on windows, be careful at the XOOPS_ROOT_PATH defined in mainfile.php, make it all lowercase will be safe.
As that reason even the newbb2 will probably cause the problem too!

Hi! sorry, these day is our national day, so I'm on vacation. Now I'm back.
:)
I mean that just replace all contents in the /modules/newbb/include/notification.php (not the newbb\functions.php) with the following codes :

I just got this problem, and solve it by the following method:

you can modify the modules/newbb/include/notification.php
libk this:
<?php
if ( !defined('NEWBB_NOTIFY_ITEMINFO') ) {
define('NEWBB_NOTIFY_ITEMINFO', 1);
function newbb_notify_iteminfo($category, $item_id)
{
$module_handler =& xoops_gethandler('module');
$module =& $module_handler->getByDirname('newbb');

if ($category=='global') {
$item['name'] = '';
$item['url'] = '';
return $item;
}
global $xoopsDB;
if ($category=='forum') {
// Assume we have a valid forum id
$sql = 'SELECT forum_name FROM ' . $xoopsDB->prefix('bb_forums') . ' WHERE forum_id = '.$item_id;
$result = $xoopsDB->query($sql); // TODO: error check
$result_array = $xoopsDB->fetchArray($result);
$item['name'] = $result_array['forum_name'];
$item['url'] = XOOPS_URL . '/modules/' . $module->getVar('dirname') . '/viewforum.php?forum=' . $item_id;
return $item;
}

if ($category=='thread') {
// Assume we have a valid topid id
$sql = 'SELECT t.topic_title,f.forum_id,f.forum_name FROM '.$xoopsDB->prefix('bb_topics') . ' t, ' . $xoopsDB->prefix('bb_forums') . ' f WHERE t.forum_id = f.forum_id AND t.topic_id = '. $item_id . ' limit 1';
$result = $xoopsDB->query($sql); // TODO: error check
$result_array = $xoopsDB->fetchArray($result);
$item['name'] = $result_array['topic_title'];
$item['url'] = XOOPS_URL . '/modules/' . $module->getVar('dirname') . '/viewtopic.php?forum=' . $result_array['forum_id'] . '&topic_id=' . $item_id;
return $item;
}

if ($category=='post') {
// Assume we have a valid post id
$sql = 'SELECT subject,topic_id,forum_id FROM ' . $xoopsDB->prefix('bb_posts') . ' WHERE post_id = ' . $item_id . ' LIMIT 1';
$result = $xoopsDB->query($sql);
$result_array = $xoopsDB->fetchArray($result);
$item['name'] = $result_array['subject'];
$item['url'] = XOOPS_URL . '/modules/' . $module->getVar('dirname') . '/viewtopic.php?forum= ' . $result_array['forum_id'] . '&topic_id=' . $result_array['topic_id'] . '#forumpost' . $item_id;
return $item;
}
}
}

wish this will help you!
btw. I think you run XOOPS on windows, is that right?