Trust Relationship, Server 2008

Greetings,

I have a client that is using SBS2003 and recently installed a 2008 server.
The 2008 server is a simple file server. All domain roles are still housed
on SBS2003. IP6 is disabled on all devices. Remote clients connect VPN
through SBS2003's RRAS.

The problem I am having is that when a user on Windows 7 VPNs into the
network they cannot access \\2008server. Instead they receive;

\\2008server is not accessible. You might not have permission to use this
network resource. Contact the administrator of this server to find out if
you have access permissions. The trust relationship between this workstation
and the primary domain failed.

The user definitely has permissions and can access \\SBS2003 no problem.
Most fixes recommend rejoining the PC to the domain. Being these are mobile
users, most of them have home operating system and cannot join a domain.
Secondly this problem started and is only with Server 2008. None of my
Windows XP users have reported any problems accessing data.

My assumption is that there is some sort of security setting in place on
Server 2008 that would need to be modified to allow these machines to work.

I am hoping that someone can shed some insight on how I can put a work
around in place so my Windows 7 clients can access Server 2008's shares.

Thanks for your time.