Joomla 2.5.8 / Hikashop 2 problems

We have upgraded to Joomla 2.5.8 and Hikashop 2 business edition.

All seems to be working well. However in the back-end we cannot edit or add products. If we try this we receive an html fragment, as though routing has not succeeded.

So, this url will produce some html, but no header, footer and hikashop product editor :

administrator/index.php?option=com_hikashop&ctrl=product&task=edit&cid[]=199

Can you please suggest what we should be looking for ? This was working in Joomla 2.5.4 / Hikashop 1.6

If required I can send you the domain and login details.

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PHP Built On Linux provps.gbihosting.net 2.6.18.8-3 #2 SMP Sun Nov 21 13:30:02 PST 2010 i686
Database Version 5.5.27-cll
Database Collation utf8_general_ci
PHP Version 5.3.3
Web Server Apache/2.2.17 (Unix) mod_ssl/2.2.17 OpenSSL/0.9.8e-fips-rhel5 mod_bwlimited/1.4
WebServer to PHP Interface cgi-fcgi
Joomla! Version Joomla! 2.5.8 Stable [ Ember ] 8-November-2012 14:00 GMT
Joomla! Platform Version Joomla Platform 11.4.0 Stable [ Brian Kernighan ] 03-Jan-2012 00:00 GMT
User Agent Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_2) AppleWebKit/537.11 (KHTML, like Gecko) Chrome/23.0.1271.91 Safari/537.11

Some debugging gave :

Fatal error: Call to undefined method stdClass::onDisplay() in /libraries/joomla/html/editor.php

For others, it may server to echo out the plugin being assigned here e.g.

echo '<p>problem plugin : '.$plugin->name.'</p>';

Thanks Nicolas ... I should have debugged first. Not a Hikashop issue.