HELP - EMERGENCY: 404 pages not showing

[ironlion37]

I have recently upgraded a site from Joomla 1.5 / VM 1.1.9 to Joomla 2.5.11 / VM 2.0.20b.

On the new site, malformed URLs are automatically being redirected to:

Code Select Expand

index.php?option=com_virtuemart

instead of showing a proper 404 page.

I've tried this solution: http://docs.joomla.org/Creating_a_Custom_404_Error_Page

And it has no effect.

Site traffic has dropped by at least 50% over the last week and I can't find a working solution anywhere....

Please help 

[AH]

I use this great system plugin

http://www.sistemistica.it/redj.html