diff --git a/ucs-school-s4-branch-site/ucsschool-s4-branch-site.py b/ucs-school-s4-branch-site/ucsschool-s4-branch-site.py
index d67c8581..e67ba46d 100644
--- a/ucs-school-s4-branch-site/ucsschool-s4-branch-site.py
+++ b/ucs-school-s4-branch-site/ucsschool-s4-branch-site.py
@@ -35,21 +35,21 @@ __package__ = ''		# workaround for PEP 366
 import listener
 import univention.debug as ud
 import univention.admin.uexceptions as udm_errors
-import univention.uldap
 import univention.config_registry
 
 # import s4-connector listener module code, but don't generate pyc file
 import os
 import sys
 import ldap
-sys.dont_write_bytecode = True
 import imp
-s4_connector_listener_path = '/usr/lib/univention-directory-listener/system/s4-connector.py'
-s4_connector_listener = imp.load_source('s4_connector', s4_connector_listener_path)
 from ucsschool.lib.schoolldap import LDAP_Connection, MACHINE_READ, SchoolSearchBase
 import traceback
 import subprocess
 
+sys.dont_write_bytecode = True
+s4_connector_listener_path = '/usr/lib/univention-directory-listener/system/s4-connector.py'
+s4_connector_listener = imp.load_source('s4_connector', s4_connector_listener_path)
+
 # Listener registration data
 name = 'ucsschool-s4-branch-site'
 description = 'UCS@school S4 branch site module'
@@ -76,7 +76,7 @@ def load_hooks():
 		try:
 			hook = imp.load_source(modulename, file_path)
 		except Exception as ex:
-			ud.debug(ud.LISTENER, ud.ERROR, "Error importing %s as %s:" % (file_path, modulename))
+			ud.debug(ud.LISTENER, ud.ERROR, "Error importing %s as %s: %s" % (file_path, modulename, ex))
 			ud.debug(ud.LISTENER, ud.ERROR, traceback.format_exc())
 		hooks.append(hook)
 
@@ -84,14 +84,13 @@ def load_hooks():
 
 
 def run_hooks(fname, *args):
-	global _hooks
 	for hook in _hooks:
 		if hasattr(hook, fname):
 			try:
 				hook_func = getattr(hook, fname)
 				hook_func(*args)
 			except Exception as ex:
-				ud.debug(ud.LISTENER, ud.ERROR, "Error running %s.%s():" % (hook.__name__, fname))
+				ud.debug(ud.LISTENER, ud.ERROR, "Error running %s.%s(): %s" % (hook.__name__, fname, ex))
 				ud.debug(ud.LISTENER, ud.ERROR, traceback.format_exc())
 # </Hooks handling> ##############
 
@@ -107,14 +106,13 @@ _hooks = []
 
 @LDAP_Connection(MACHINE_READ)
 def on_load(ldap_machine_read=None, ldap_position=None):
-	global _ldap_hostdn
 	global _hooks
 	_hooks = load_hooks()
 
 	global _ucsschool_service_specialization_filter
 	try:
 		res = ldap_machine_read.search(base=_ldap_hostdn, scope='base', attr=('univentionService',))
-	except udm_errors.ldapError, e:
+	except udm_errors.ldapError as e:
 		ud.debug(ud.LISTENER, ud.ERROR, '%s: Error accessing LDAP: %s' % (name, e))
 		return
 
@@ -189,7 +187,6 @@ STD_S4_SRV_RECORDS = {
 
 @LDAP_Connection(MACHINE_READ)
 def visible_samba4_school_dcs(excludeDN=None, ldap_machine_read=None, ldap_position=None):
-	global filter
 	_visible_samba4_school_dcs = []
 	try:
 		res = ldap_machine_read.search(base=ldap_position.getDn(), filter=filter, attr=['cn', 'associatedDomain'])
@@ -201,18 +198,14 @@ def visible_samba4_school_dcs(excludeDN=None, ldap_machine_read=None, ldap_posit
 				else:
 					domainname = _local_domainname
 				_visible_samba4_school_dcs.append('.'.join((obj['cn'][0], domainname)))
-	except udm_errors.ldapError, e:
+	except udm_errors.ldapError as e:
 		ud.debug(ud.LISTENER, ud.ERROR, '%s: Error accessing LDAP: %s' % (name, e))
 
 	return _visible_samba4_school_dcs
 
 
 def update_ucr_overrides(excludeDN=None):
-	global STD_S4_SRV_RECORDS
-	global _record_type
-	global _local_domainname
 	global _s4_connector_restart
-	global _relativeDomainName_trigger_set
 
 	server_fqdn_list = visible_samba4_school_dcs(excludeDN=excludeDN)
 	server_fqdn_list.sort()
@@ -299,10 +292,6 @@ def update_ucr_overrides(excludeDN=None):
 
 @LDAP_Connection(MACHINE_READ)
 def trigger_sync_ucs_to_s4(ldap_machine_read=None, ldap_position=None):
-	global _record_type
-	global _local_domainname
-	global _relativeDomainName_trigger_set
-
 	for relativeDomainName in list(_relativeDomainName_trigger_set):
 		# trigger S4 Connector
 		ldap_filter = '(&(univentionObjectType=dns/%s)(zoneName=%s)(relativeDomainName=%s))' % (_record_type, _local_domainname, relativeDomainName)
@@ -312,7 +301,7 @@ def trigger_sync_ucs_to_s4(ldap_machine_read=None, ldap_position=None):
 			for (record_dn, obj) in res:
 				s4_connector_listener.handler(record_dn, obj, obj, 'm')
 				_relativeDomainName_trigger_set.remove(relativeDomainName)
-		except udm_errors.ldapError, e:
+		except udm_errors.ldapError as e:
 			ud.debug(ud.LISTENER, ud.ERROR, '%s: Error accessing LDAP: %s' % (name, e))
 
 
@@ -369,7 +358,6 @@ def handler(dn, new, old, command):
 
 def postrun():
 	global _s4_connector_restart
-	global _relativeDomainName_trigger_set
 
 	if not listener.configRegistry.is_true('connector/s4/autostart', True):
 		univention.debug.debug(univention.debug.LISTENER, univention.debug.PROCESS, '%s: S4 Connector restart skipped, disabled via connector/s4/autostart.' % (name,))