Upgraded to 3.3, I get stuck in a loop too:
2013/12/20 09:10:41 WARN> User.pm:507 EBox::Samba::User::addToZentyal - The user Guest doesn't have credentials!
2013/12/20 09:10:41 INFO> User.pm:455 EBox::Samba::User::addToZentyal - Adding samba user 'krbtgt' to Zentyal
2013/12/20 09:10:41 DEBUG> LdapObject.pm:657 EBox::Users::LdapObject::checkCN - There exists already a object of type utilisateur with CN=- - in this container at Trace begun at /usr/share/perl5/EBox/Exceptions/Base.pm line 79
EBox::Exceptions::Base::stacktrace('EBox::Exceptions::External=HASH(0x5ea2f50)') called at /usr/share/perl5/EBox/Exceptions/Base.pm line 119
EBox::Exceptions::Base::log('EBox::Exceptions::External=HASH(0x5ea2f50)') called at /usr/share/perl5/EBox/Exceptions/External.pm line 43
EBox::Exceptions::External::new('EBox::Exceptions::External', 'There exists already a object of type utilisateur with CN=- - in this container') called at /usr/share/perl5/EBox/Exceptions/Base.pm line 91
EBox::Exceptions::Base::throw('EBox::Exceptions::External', 'There exists already a object of type utilisateur with CN=- - in this container') called at /usr/share/perl5/EBox/Users/LdapObject.pm line 657
EBox::Users::LdapObject::checkCN('EBox::Users::User', 'EBox::Users::OU=HASH(0x5e9e048)', '- -') called at /usr/share/perl5/EBox/Users/User.pm line 514
EBox::Users::User::create('EBox::Users::User', 'initials', undef, 'parent', 'EBox::Users::OU=HASH(0x5e9e048)', 'uid', 'krbtgt', 'uidNumber', 3000043, 'ignoreMods', 'ARRAY(0x5e92570)', 'description', 'Key Distribution Center Service Account', 'isInternal', 1, 'surname', '-', 'givenname', '-', 'fullname', 'krbtgt', 'displayname', undef, 'isSystemUser', '') called at /usr/share/perl5/EBox/Samba/User.pm line 480
eval {...} at /usr/share/perl5/EBox/Samba/User.pm line 456
EBox::Samba::User::addToZentyal('EBox::Samba::User=HASH(0x4ad3c48)') called at /usr/share/zentyal-samba/s4sync line 183
eval {...} at /usr/share/zentyal-samba/s4sync line 182
2013/12/20 09:10:41 ERROR> User.pm:485 EBox::Samba::User::addToZentyal - Error loading user 'krbtgt': There exists already a object of type utilisateur with CN=- - in this container
2013/12/20 09:11:15 INFO> User.pm:455 EBox::Samba::User::addToZentyal - Adding samba user 'dns-zen' to Zentyal
2013/12/20 09:11:18 DEBUG> Samba.pm:2398 EBox::Samba::ldbObjectByObjectGUID - Missing argument: objectGUID at Trace begun at /usr/share/perl5/EBox/Exceptions/Base.pm line 79
EBox::Exceptions::Base::stacktrace('EBox::Exceptions::MissingArgument=HASH(0x63e0e30)') called at /usr/share/perl5/EBox/Exceptions/Base.pm line 119
EBox::Exceptions::Base::log('EBox::Exceptions::MissingArgument=HASH(0x63e0e30)') called at /usr/share/perl5/EBox/Exceptions/External.pm line 43
EBox::Exceptions::External::new('EBox::Exceptions::MissingArgument', 'Missing argument: objectGUID') called at /usr/share/perl5/EBox/Exceptions/MissingArgument.pm line 50
EBox::Exceptions::MissingArgument::new('EBox::Exceptions::MissingArgument', 'objectGUID') called at /usr/share/perl5/EBox/Exceptions/Base.pm line 91
EBox::Exceptions::Base::throw('EBox::Exceptions::MissingArgument', 'objectGUID') called at /usr/share/perl5/EBox/Samba.pm line 2398
EBox::Samba::ldbObjectByObjectGUID('EBox::Samba=HASH(0x500d970)') called at /usr/share/perl5/EBox/Users.pm line 1147
EBox::Users::userExists('EBox::Users=HASH(0x5048968)', 'dns-zen') called at /usr/share/perl5/EBox/Users/User.pm line 492
EBox::Users::User::create('EBox::Users::User', 'initials', undef, 'parent', 'EBox::Users::OU=HASH(0x51d55b0)', 'uid', 'dns-zen', 'uidNumber', 3000042, 'ignoreMods', 'ARRAY(0x51d4ae8)', 'description', 'DNS Service Account for zen', 'surname', '-', 'givenname', '-', 'fullname', 'dns-zen', 'displayname', undef, 'isSystemUser', '') called at /usr/share/perl5/EBox/Samba/User.pm line 480
eval {...} at /usr/share/perl5/EBox/Samba/User.pm line 456
EBox::Samba::User::addToZentyal('EBox::Samba::User=HASH(0x50d10b0)') called at /usr/share/zentyal-samba/s4sync line 183
eval {...} at /usr/share/zentyal-samba/s4sync line 182
2013/12/20 09:11:18 ERROR> User.pm:485 EBox::Samba::User::addToZentyal - Error loading user 'dns-zen': Missing argument: objectGUID
2013/12/20 09:11:18 INFO> User.pm:455 EBox::Samba::User::addToZentyal - Adding samba user 'lox' to Zentyal
2013/12/20 09:11:19 DEBUG> User.pm:493 EBox::Users::User::create - user name lox existe déjà. at Trace begun at /usr/share/perl5/EBox/Exceptions/Base.pm line 79
EBox::Exceptions::Base::stacktrace('EBox::Exceptions::DataExists=HASH(0x51f3718)') called at /usr/share/perl5/EBox/Exceptions/Base.pm line 119
EBox::Exceptions::Base::log('EBox::Exceptions::DataExists=HASH(0x51f3718)') called at /usr/share/perl5/EBox/Exceptions/External.pm line 43
EBox::Exceptions::External::new('EBox::Exceptions::DataExists', 'user name lox existe dM-ijM-`.', 'data', 'user name', 'value', 'lox') called at /usr/share/perl5/EBox/Exceptions/DataExists.pm line 56
EBox::Exceptions::DataExists::new('EBox::Exceptions::DataExists', 'data', 'user name', 'value', 'lox') called at /usr/share/perl5/EBox/Exceptions/Base.pm line 91
EBox::Exceptions::Base::throw('EBox::Exceptions::DataExists', 'data', 'user name', 'value', 'lox') called at /usr/share/perl5/EBox/Users/User.pm line 493
EBox::Users::User::create('EBox::Users::User', 'initials', undef, 'parent', 'EBox::Users::OU=HASH(0x6452050)', 'uid', 'lox', 'uidNumber', 3000041, 'ignoreMods', 'ARRAY(0x51ed200)', 'description', undef, 'surname', 'Dinclaux', 'givenname', 'Laurent', 'fullname', 'Laurent Dinclaux', 'displayname', undef, 'isSystemUser', '') called at /usr/share/perl5/EBox/Samba/User.pm line 480
eval {...} at /usr/share/perl5/EBox/Samba/User.pm line 456
EBox::Samba::User::addToZentyal('EBox::Samba::User=HASH(0x50d1500)') called at /usr/share/zentyal-samba/s4sync line 183
eval {...} at /usr/share/zentyal-samba/s4sync line 182
2013/12/20 09:11:19 INFO> User.pm:455 EBox::Samba::User::addToZentyal - Adding samba user 'Guest' to Zentyal
2013/12/20 09:11:19 DEBUG> User.pm:493 EBox::Users::User::create - user name Guest existe déjà. at Trace begun at /usr/share/perl5/EBox/Exceptions/Base.pm line 79
EBox::Exceptions::Base::stacktrace('EBox::Exceptions::DataExists=HASH(0x63dfd10)') called at /usr/share/perl5/EBox/Exceptions/Base.pm line 119
EBox::Exceptions::Base::log('EBox::Exceptions::DataExists=HASH(0x63dfd10)') called at /usr/share/perl5/EBox/Exceptions/External.pm line 43
EBox::Exceptions::External::new('EBox::Exceptions::DataExists', 'user name Guest existe dM-ijM-`.', 'data', 'user name', 'value', 'Guest') called at /usr/share/perl5/EBox/Exceptions/DataExists.pm line 56
EBox::Exceptions::DataExists::new('EBox::Exceptions::DataExists', 'data', 'user name', 'value', 'Guest') called at /usr/share/perl5/EBox/Exceptions/Base.pm line 91
EBox::Exceptions::Base::throw('EBox::Exceptions::DataExists', 'data', 'user name', 'value', 'Guest') called at /usr/share/perl5/EBox/Users/User.pm line 493
EBox::Users::User::create('EBox::Users::User', 'initials', undef, 'parent', 'EBox::Users::OU=HASH(0x649fce0)', 'uid', 'Guest', 'uidNumber', 65534, 'ignoreMods', 'ARRAY(0x63df740)', 'description', 'Built-in account for guest access to the computer/domain', 'surname', '-', 'givenname', '-', 'fullname', 'Guest', 'displayname', undef, 'isSystemUser', '') called at /usr/share/perl5/EBox/Samba/User.pm line 480
eval {...} at /usr/share/perl5/EBox/Samba/User.pm line 456
EBox::Samba::User::addToZentyal('EBox::Samba::User=HASH(0x50d5cc0)') called at /usr/share/zentyal-samba/s4sync line 183
eval {...} at /usr/share/zentyal-samba/s4sync line 182
2013/12/20 09:11:19 WARN> User.pm:507 EBox::Samba::User::addToZentyal - The user Guest doesn't have credentials!
2013/12/20 09:11:19 INFO> User.pm:455 EBox::Samba::User::addToZentyal - Adding samba user 'krbtgt' to Zentyal
2013/12/20 09:11:19 DEBUG> LdapObject.pm:657 EBox::Users::LdapObject::checkCN - There exists already a object of type utilisateur with CN=- - in this container at Trace begun at /usr/share/perl5/EBox/Exceptions/Base.pm line 79
EBox::Exceptions::Base::stacktrace('EBox::Exceptions::External=HASH(0x64a51a0)') called at /usr/share/perl5/EBox/Exceptions/Base.pm line 119
EBox::Exceptions::Base::log('EBox::Exceptions::External=HASH(0x64a51a0)') called at /usr/share/perl5/EBox/Exceptions/External.pm line 43
EBox::Exceptions::External::new('EBox::Exceptions::External', 'There exists already a object of type utilisateur with CN=- - in this container') called at /usr/share/perl5/EBox/Exceptions/Base.pm line 91
EBox::Exceptions::Base::throw('EBox::Exceptions::External', 'There exists already a object of type utilisateur with CN=- - in this container') called at /usr/share/perl5/EBox/Users/LdapObject.pm line 657
EBox::Users::LdapObject::checkCN('EBox::Users::User', 'EBox::Users::OU=HASH(0x64a0298)', '- -') called at /usr/share/perl5/EBox/Users/User.pm line 514
EBox::Users::User::create('EBox::Users::User', 'initials', undef, 'parent', 'EBox::Users::OU=HASH(0x64a0298)', 'uid', 'krbtgt', 'uidNumber', 3000043, 'ignoreMods', 'ARRAY(0x64947c0)', 'description', 'Key Distribution Center Service Account', 'isInternal', 1, 'surname', '-', 'givenname', '-', 'fullname', 'krbtgt', 'displayname', undef, 'isSystemUser', '') called at /usr/share/perl5/EBox/Samba/User.pm line 480
eval {...} at /usr/share/perl5/EBox/Samba/User.pm line 456
EBox::Samba::User::addToZentyal('EBox::Samba::User=HASH(0x50d5c78)') called at /usr/share/zentyal-samba/s4sync line 183
eval {...} at /usr/share/zentyal-samba/s4sync line 182
2013/12/20 09:11:19 ERROR> User.pm:485 EBox::Samba::User::addToZentyal - Error loading user 'krbtgt': There exists already a object of type utilisateur with CN=- - in this container