[Typo3] 404 Error Page Handling gives error!

[Simon Child]

I'm trying to use extension  404 Error Page Handling.

I have followed the instructions, including setting up domain and a page to
redirect to (I've tried both a page within Typo3 pagetree, and an external
php file), etc.

I'm using Typo3 3.8.0, I have noted the note in the manual to change one
line in the code - change  $TSFE->connectToMySQL(); to...
$TSFE->connectToDB();

But whether I change this or not doesn't help. Problems:

1) The script 404page_not_found.php is clearly being launched:

e.g. if I try an invalid url such as www.mydomain.org/index.php?id=10000 I
get an email from 404 Error Page Handling with the details of the incorrect
url.

But the browser shows me a Typo3 page:

=================
Error!

The requested page did not exist or was inaccessible. For this domain
mydomain.org no error-page is defined. Please check the domain-records.
=================


2) If I try a different type of invalid URL such as
http://mydomain.org/indefff I get:

=================
Fatal error: Call to a member function on a non-object in

/(path)/typo3_src-3.8.0/typo3/sysext/cms/tslib/class.tslib_fe.php on line
413
=================

I also get the same message if I go direct to
http://mydomain.org/404page_not_found.php


I'm not using RealURL or simulatestatic.

Suggestions please. I am ready to launch a large site (300 pages) which I
have converted to Typo3, and I want to catch all 404's looking for the old
page structure so that I can setup any redirects that I may have missed.

-- 
Simon Child