Index: ucs-school-umc-computerroom/umc/python/computerroom/__init__.py
===================================================================
--- ucs-school-umc-computerroom/umc/python/computerroom/__init__.py	(Revision 58114)
+++ ucs-school-umc-computerroom/umc/python/computerroom/__init__.py	(Arbeitskopie)
@@ -778,7 +778,7 @@
 			# remove empty items ('""') in list
 			vset[varname] = ' '.join([x for x in vset[varname].split(' ') if x != '""'])
 		if varname in vunset:
-			del vunset[varname]
+			vunset.remove(varname)
 
 		# set values
 		ucr_vars = sorted(map(lambda x: '%s=%s' % x, vset.items()))