404 after enabling SEF urls

[bzh]

Joomla 1.5.25
Virtuemart 2.0.6

When I enable SEF urls in Joomla I get a 404 for anything Virtuemart. htaccess in place and non virtuemart links are working fine. SEO is enabled in Virtuemart. I have created a menu item to the Virtuemart frontpage, this gets a 500 error.

Any ideas?

[bzh]

I have cleared up the 500 error and now have a shop frontpage which works as a SEF url - still a 404 with the categories though.