I'm in the exact same situation. Finally got Master/Slave working but now can't make a user an admin of the PDC on the slave. My error code is a little different though:
A really nasty bug has occurred
Exception
Unknown error at EBox::UsersAndGroups::addUserToGroup Referral received
Trace
Unknown error at EBox::UsersAndGroups::addUserToGroup Referral received at /usr/share/perl5/EBox/Ldap.pm line 712
EBox::Ldap::_errorOnLdap('Net::LDAP::Modify=HASH(0xb7c3494)', 'HASH(0xb7bdda0)') called at /usr/share/perl5/EBox/Ldap.pm line 373
EBox::Ldap::modify('EBox::Ldap=HASH(0xa2a92a4)', 'cn=Domain Admins,ou=Groups,dc=c2istudios,dc=com', 'HASH(0xb7bdda0)') called at /usr/share/perl5/EBox/UsersAndGroups.pm line 1732
EBox::UsersAndGroups::addUserToGroup('EBox::UsersAndGroups=HASH(0x9fdbefc)', 'ymangolds', 'Domain Admins') called at /usr/share/perl5/EBox/Samba.pm line 844
EBox::Samba::setAdminUser('EBox::Samba=HASH(0xa793e94)', 'ymangolds', 'yes') called at /usr/share/perl5/EBox/CGI/Samba/ActiveSharing.pm line 79
EBox::CGI::Samba::ActiveSharing::_user('EBox::CGI::Samba::ActiveSharing=HASH(0xb7eac5c)') called at /usr/share/perl5/EBox/CGI/Samba/ActiveSharing.pm line 86
EBox::CGI::Samba::ActiveSharing::_process('EBox::CGI::Samba::ActiveSharing=HASH(0xb7eac5c)') called at /usr/share/perl5/EBox/CGI/Base.pm line 262
EBox::CGI::Base::run('EBox::CGI::Samba::ActiveSharing=HASH(0xb7eac5c)') called at /usr/share/perl5/EBox/CGI/Run.pm line 120
EBox::CGI::Run::run('EBox::CGI::Run', 'Samba/ActiveSharing', 'EBox') called at /usr/share/ebox/cgi/ebox.cgi line 19
ModPerl::ROOT::ModPerl::Registry::usr_share_ebox_cgi_ebox_2ecgi::handler('Apache2::RequestRec=SCALAR(0xb70c034)') called at /usr/lib/perl5/ModPerl/RegistryCooker.pm line 204
eval {...} called at /usr/lib/perl5/ModPerl/RegistryCooker.pm line 204
ModPerl::RegistryCooker::run('ModPerl::Registry=HASH(0xb791a34)') called at /usr/lib/perl5/ModPerl/RegistryCooker.pm line 170
ModPerl::RegistryCooker::default_handler('ModPerl::Registry=HASH(0xb791a34)') called at /usr/lib/perl5/ModPerl/Registry.pm line 31
ModPerl::Registry::handler('ModPerl::Registry', 'Apache2::RequestRec=SCALAR(0xb70c034)') called at -e line 0
eval {...} called at -e line 0