The Outlook Web Access problem is a permissions problem. Outlook Web users must be granted "Access this computer from the network" and "Log on locally" permissions through User Manager for Domains.
See
http://support.microsoft.com/default.aspx?scid=KB;EN-US;Q175892&
and
http://support.microsoft.com/default.aspx?scid=KB;EN-US;Q245715&
Create a new Global Group called "Outlook Web Users". Add your OW users to this group.
In User Manager for Domains, Policies, User Rights, add the "Outlook Web Users" group to the "Access this computer from the network" and "Log on locally" rights.
Good luck!