Guest Checkout not working

[crystalm28]

Joomla 2.5.8
VM 2.0.18a

Customers can register and check out...but when the click the Guest checkout, the page goes back to the cart with no address?  I had someone help and his notes are...

checked on a clean install  - does work
checked your config against my clean install  - identical
checked with SEF all off - doesn't work
when saved it redirects to the cart (as it should) but gets a 303 (http://www.checkupdown.com/status/E303.html)  -
an error that no one really understands :-(
and goes back to the registration screen (sometimes) or doesn't save address
the _Session is empty - the address should be there
Test site regged as guest

Menu and model set to public...and tried disabling many modules/menus/plugins with no luck.  This one has me puzzled Help