after the entry of "/etc/init.d/zentyal webadmin restart" i got the following output in /var/log/zentyal/zentyal.log:
2014/04/16 07:04:04 DEBUG> Sudo.pm:189 EBox::Sudo::_root - /etc/init.d/zentyal webadmin restart (pid: 20311) - /sbin/status 'ebox.redis'
2014/04/16 07:04:04 INFO> Service.pm:995 EBox::Module::Service::restartService - Restarting service for module: webadmin
2014/04/16 07:04:06 DEBUG> Menu.pm:62 EBox::Menu::getKeywords - No model found for Users/Tree/Manage
2014/04/16 07:04:06 DEBUG> Sudo.pm:189 EBox::Sudo::_root - /etc/init.d/zentyal webadmin restart (pid: 20311) - set -e
/bin/mv /var/lib/zentyal/tmp/bbeZLvqtKq '/var/lib/zentyal/conf/nginx.conf'
/bin/chmod 0644 '/var/lib/zentyal/conf/nginx.conf'
/bin/chown ebox.ebox '/var/lib/zentyal/conf/nginx.conf'
2014/04/16 07:04:06 DEBUG> Sudo.pm:189 EBox::Sudo::_root - /etc/init.d/zentyal webadmin restart (pid: 20311) - set -e
/bin/mv /var/lib/zentyal/tmp/q1y7YARZxl '/etc/init/zentyal.webadmin-nginx.conf'
/bin/chmod 0644 '/etc/init/zentyal.webadmin-nginx.conf'
/bin/chown 0.0 '/etc/init/zentyal.webadmin-nginx.conf'
2014/04/16 07:04:06 DEBUG> Sudo.pm:189 EBox::Sudo::_root - /etc/init.d/zentyal webadmin restart (pid: 20311) - set -e
/bin/mv /var/lib/zentyal/tmp/qBc_iViqHu '/etc/init/zentyal.webadmin-uwsgi.conf'
/bin/chmod 0644 '/etc/init/zentyal.webadmin-uwsgi.conf'
/bin/chown 0.0 '/etc/init/zentyal.webadmin-uwsgi.conf'
2014/04/16 07:04:06 DEBUG> Sudo.pm:189 EBox::Sudo::_root - /etc/init.d/zentyal webadmin restart (pid: 20311) - set -e
/bin/mv /var/lib/zentyal/tmp/UbjkmkBn3I '/var/lib/zentyal/dynamicwww//css/public.css'
/bin/chmod 0644 '/var/lib/zentyal/dynamicwww//css/public.css'
/bin/chown 107.112 '/var/lib/zentyal/dynamicwww//css/public.css'
2014/04/16 07:04:06 DEBUG> Sudo.pm:189 EBox::Sudo::_root - /etc/init.d/zentyal webadmin restart (pid: 20311) - set -e
/bin/mv /var/lib/zentyal/tmp/1cA9ZIFdv0 '/var/lib/zentyal/dynamicwww//css/login.css'
/bin/chmod 0644 '/var/lib/zentyal/dynamicwww//css/login.css'
/bin/chown 107.112 '/var/lib/zentyal/dynamicwww//css/login.css'
2014/04/16 07:04:06 DEBUG> Sudo.pm:189 EBox::Sudo::_root - /etc/init.d/zentyal webadmin restart (pid: 20311) - set -e
/bin/mv /var/lib/zentyal/tmp/uT2xX8SnKx '/usr/share/zentyal/www//css/jquery-ui/jquery-ui.css'
/bin/chmod 0644 '/usr/share/zentyal/www//css/jquery-ui/jquery-ui.css'
/bin/chown 107.112 '/usr/share/zentyal/www//css/jquery-ui/jquery-ui.css'
2014/04/16 07:04:06 DEBUG> Sudo.pm:189 EBox::Sudo::_root - /etc/init.d/zentyal webadmin restart (pid: 20311) - rm -f /var/lib/zentyal/tmp/webadmin_no_restart_on_trigger
2014/04/16 07:04:06 DEBUG> Sudo.pm:189 EBox::Sudo::_root - /etc/init.d/zentyal webadmin restart (pid: 20311) - sed -i 's/^enabled=.*/enabled=1/' /etc/default/apport
2014/04/16 07:04:06 DEBUG> Sudo.pm:189 EBox::Sudo::_root - /etc/init.d/zentyal webadmin restart (pid: 20311) - /sbin/status 'zentyal.webadmin-uwsgi'
2014/04/16 07:04:06 DEBUG> Sudo.pm:189 EBox::Sudo::_root - /etc/init.d/zentyal webadmin restart (pid: 20311) - /sbin/stop 'zentyal.webadmin-uwsgi'
2014/04/16 07:04:06 DEBUG> Sudo.pm:189 EBox::Sudo::_root - /etc/init.d/zentyal webadmin restart (pid: 20311) - /sbin/start 'zentyal.webadmin-uwsgi'
2014/04/16 07:04:06 DEBUG> Sudo.pm:189 EBox::Sudo::_root - /etc/init.d/zentyal webadmin restart (pid: 20311) - /sbin/status 'zentyal.webadmin-nginx'
2014/04/16 07:04:06 DEBUG> Sudo.pm:189 EBox::Sudo::_root - /etc/init.d/zentyal webadmin restart (pid: 20311) - /sbin/start 'zentyal.webadmin-nginx'
2014/04/16 07:04:06 ERROR> Sudo.pm:240 EBox::Sudo::_rootError - root command /sbin/start 'zentyal.webadmin-nginx' failed.
Error output: start: Job failed to start
Command output: .
Exit value: 1 at root command /sbin/start 'zentyal.webadmin-nginx' failed.
Error output: start: Job failed to start
Command output: .
Exit value: 1 at /usr/share/perl5/EBox/Sudo.pm line 240
EBox::Sudo::_rootError('/usr/bin/sudo -p sudo: /var/lib/zentyal/tmp/9s4z4lXeUW.cmd 2> /var/lib/zentyal/tmp/stderr', '/sbin/start \'zentyal.webadmin-nginx\'', 256, 'ARRAY(0xc63a374)', 'ARRAY(0x94fa7d4)') called at /usr/share/perl5/EBox/Sudo.pm line 210
EBox::Sudo::_root(1, '/sbin/start \'zentyal.webadmin-nginx\'') called at /usr/share/perl5/EBox/Sudo.pm line 153
EBox::Sudo::root('/sbin/start \'zentyal.webadmin-nginx\'') called at /usr/share/perl5/EBox/Service.pm line 52
EBox::Service::manage('zentyal.webadmin-nginx', 'restart') called at /usr/share/perl5/EBox/WebAdmin.pm line 118
EBox::WebAdmin::_manageNginx('EBox::WebAdmin=HASH(0xa0d7d98)', 'restart') called at /usr/share/perl5/EBox/WebAdmin.pm line 104
EBox::WebAdmin::_daemon('EBox::WebAdmin=HASH(0xa0d7d98)', 'restart') called at /usr/share/perl5/EBox/WebAdmin.pm line 182
EBox::WebAdmin::_enforceServiceState('EBox::WebAdmin=HASH(0xa0d7d98)', 'restart', 1, 'restartModules', 1) called at /usr/share/perl5/EBox/Module/Service.pm line 977
EBox::Module::Service::_regenConfig('EBox::WebAdmin=HASH(0xa0d7d98)', 'restart', 1, 'restartModules', 1) called at /usr/share/perl5/EBox/Module/Service.pm line 997
eval {...} at /usr/share/perl5/EBox/Module/Service.pm line 996
EBox::Module::Service::restartService('EBox::WebAdmin=HASH(0xa0d7d98)', 'restartModules', 1) called at /usr/share/perl5/EBox/Util/Init.pm line 129
eval {...} at /usr/share/perl5/EBox/Util/Init.pm line 127
EBox::Util::Init::moduleAction('webadmin', 'restartService', 'restart') called at /usr/share/perl5/EBox/Util/Init.pm line 255
EBox::Util::Init::moduleRestart('webadmin') called at /etc/init.d/zentyal line 58
main::main at /etc/init.d/zentyal line 79
2014/04/16 07:04:06 ERROR> Service.pm:999 EBox::Module::Service::restartService - Error restarting service: root command /sbin/start 'zentyal.webadmin-nginx' failed.
Error output: start: Job failed to start
Command output: .
Exit value: 1
2014/04/16 07:04:06 ERROR> Service.pm:1001 EBox::Module::Service::restartService - root command /sbin/start 'zentyal.webadmin-nginx' failed.
Error output: start: Job failed to start
Command output: .
Exit value: 1 at root command /sbin/start 'zentyal.webadmin-nginx' failed.
Error output: start: Job failed to start
Command output: .
Exit value: 1 at /usr/share/perl5/EBox/Module/Service.pm line 1001
EBox::Module::Service::restartService('EBox::WebAdmin=HASH(0xa0d7d98)', 'restartModules', 1) called at /usr/share/perl5/EBox/Util/Init.pm line 129
eval {...} at /usr/share/perl5/EBox/Util/Init.pm line 127
EBox::Util::Init::moduleAction('webadmin', 'restartService', 'restart') called at /usr/share/perl5/EBox/Util/Init.pm line 255
EBox::Util::Init::moduleRestart('webadmin') called at /etc/init.d/zentyal line 58
main::main at /etc/init.d/zentyal line 79