Problem:
According to Bug 47314 there were some changes for cross-domains. This hit unjoined Clients to.
Unjoined Windows Clients cannot access fileshares on a memberserver
Solution:
To get the shareaccess work again with unjoined clients you have to set these ucr variable on all samba domaincontrollers.
ucr set samba/global/options/"auth methods"="sam winbind sam_ignoredomain"
/etc/init.d/samba restart