--- a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/domaincontroller_backup.py	
+++ a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/domaincontroller_backup.py	
@@ -428,7 +428,7 @@ def open(self):
 
 		tmppos=univention.admin.uldap.position(self.position.getDomain())
 
-		if self.dn:
+		if self.exists():
 
 			if 'posix' in self.options and not self.info.get( 'primaryGroup' ):
 				primaryGroupNumber=self.oldattr.get('gidNumber',[''])[0]
--- a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/domaincontroller_master.py	
+++ a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/domaincontroller_master.py	
@@ -427,7 +427,7 @@ def open(self):
 		self.oldPrimaryGroupDn=0
 
 
-		if self.dn:
+		if self.exists():
 
 			if 'posix' in self.options and not self.info.get( 'primaryGroup' ):
 				primaryGroupNumber=self.oldattr.get('gidNumber',[''])[0]
--- a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/domaincontroller_slave.py	
+++ a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/domaincontroller_slave.py	
@@ -429,7 +429,7 @@ def open(self):
 
 		tmppos=univention.admin.uldap.position(self.position.getDomain())
 
-		if self.dn:
+		if self.exists():
 
 			if 'posix' in self.options and not self.info.get( 'primaryGroup' ):
 				primaryGroupNumber=self.oldattr.get('gidNumber',[''])[0]
--- a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/ipmanagedclient.py	
+++ a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/ipmanagedclient.py	
@@ -261,7 +261,7 @@ def open(self):
 		univention.admin.handlers.simpleComputer.open( self )
 		self.nagios_open()
 
-		if not self.dn:
+		if not self.exists():
 			return
 
 		self.save()
--- a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/linux.py	
+++ a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/linux.py	
@@ -374,7 +374,7 @@ def open(self):
 		self.modifypassword=0
 
 
-		if self.dn:
+		if self.exists():
 
 			if 'posix' in self.options and not self.info.get( 'primaryGroup' ):
 				primaryGroupNumber=self.oldattr.get('gidNumber',[''])[0]
--- a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/macos.py	
+++ a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/macos.py	
@@ -389,7 +389,7 @@ def open(self):
 
 		tmppos=univention.admin.uldap.position(self.position.getDomain())
 
-		if self.dn:
+		if self.exists():
 
 			if 'posix' in self.options and not self.info.get( 'primaryGroup' ):
 				primaryGroupNumber=self.oldattr.get('gidNumber',[''])[0]
--- a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/memberserver.py	
+++ a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/memberserver.py	
@@ -418,7 +418,7 @@ def open(self):
 		self.newPrimaryGroupDn=0
 		self.oldPrimaryGroupDn=0
 
-		if self.dn:
+		if self.exists():
 
 			if 'posix' in self.options and not self.info.get( 'primaryGroup' ):
 				primaryGroupNumber=self.oldattr.get('gidNumber',[''])[0]
--- a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/trustaccount.py	
+++ a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/trustaccount.py	
@@ -119,7 +119,7 @@ def open(self):
 
 		self.options=['samba']
 		self.modifypassword=1
-		if self.dn:
+		if self.exists():
 			self['password']='********'
 			self.modifypassword=0
 
--- a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/ubuntu.py	
+++ a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/ubuntu.py	
@@ -374,7 +374,7 @@ def open(self):
 		self.modifypassword=0
 
 
-		if self.dn:
+		if self.exists():
 
 			if 'posix' in self.options and not self.info.get( 'primaryGroup' ):
 				primaryGroupNumber=self.oldattr.get('gidNumber',[''])[0]
--- a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/windows.py	
+++ a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/windows.py	
@@ -406,7 +406,7 @@ def open(self):
 
 		tmppos=univention.admin.uldap.position(self.position.getDomain())
 
-		if self.dn:
+		if self.exists():
 
 			if 'posix' in self.options and not self.info.get( 'primaryGroup' ):
 				primaryGroupNumber=self.oldattr.get('gidNumber',[''])[0]
--- a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/windows_domaincontroller.py	
+++ a/ucs-4.0-0/management/univention-directory-manager-modules/modules/univention/admin/handlers/computers/windows_domaincontroller.py	
@@ -415,7 +415,7 @@ def open(self):
 
 		tmppos=univention.admin.uldap.position(self.position.getDomain())
 
-		if self.dn:
+		if self.exists():
 
 			if 'posix' in self.options and not self.info.get( 'primaryGroup' ):
 				primaryGroupNumber=self.oldattr.get('gidNumber',[''])[0]