Well, the error on your site now looks different:
Warning: main(/includes/version.php) [function.main]: failed to open stream: No such file or directory in /home/sites/lantastic.co.uk/public_html/includes/joomla.php on line 71
Fatal error: main() [function.require]: Failed opening required '/includes/version.php' (include_path='.:/usr/share/pear'

in /home/sites/lantastic.co.uk/public_html/includes/joomla.php on line 71
Originally, it was unable to find the joomla.php, seems like you fixed something there?
But now joomla.php fails to find the version.php. Line 71 in joomla.php reads:
require_once( $mosConfig_absolute_path . '/includes/version.php' );
Can you insure that $mosConfig_absolute_path is defined correctly? You can test this by adding this line to the mls_seatmap.ajax.php just below the line with "...globals.php":
die($mosConfig_absolute_path . '/includes/joomla.php'

;
When you then go to the link again it should display:
/home/sites/lantastic.co.uk/public_html/includes/joomla.php
Is this the case?