Hello;
I have set "404 page" to custom 404 page. But some page redirect to the home page and/or never send 404 state. I dont know if i must post this problem to Artio or Virtuemart. Webmaster tool send me 'augmentation du nombre d'erreurs de type "soft 404"'.

Ask me for more information .

Hello,

The problem is that by default if JoomSEF doesn't find the SEF URL in its database, Joomla tries to handle it and usually displays some page.
This can be fixed by disabling the "Parse Joomla SEO links" option in JoomSEF's Configuration on the Advanced tab. However, if you use "Default Joomla router" or "Component's own router" as Active handler for some component, its URLs won't work.

Thanks. Now (and that already that before) I show 404 error pages but the page state is 301(redirect) or 200(ok). So Google continue to send me mail for 'soft 404' problem. can you help me please ?

In that case the 404 page is most likely not displayed by JoomSEF, because JoomSEF always sends the 404 code when it displayes the 404 page.
Check if you have some 301 redirects set up in JoomSEF and check whether the System - ARTIO JoomSEF plugin is ordered as the first of system plugins.