It's official RH Bugzilla Bug #428301:

http://bugzilla.redhat.com/show_bug.cgi?id=428301

Problem may be solved by this small patch:

--- system-config-users-1.2.51/src/userWindow.py.orig   2008-04-01
17:59:41.000000000 +0400
+++ system-config-users-1.2.51/src/userWindow.py        2008-04-01
18:02:10.000000000 +0400
@@ -351,7 +351,7 @@
                 #No group currently exists with this name, so we can
create one
                 groupEnt = self.parent.ADMIN.initGroup(userName)
                 # workaround bug with purely numerical names in
ADMIN.initGroup ()
-                groupEnt.set (libuser.GROUPNAME, groupName)
+                groupEnt.set (libuser.GROUPNAME, userName)
                 groupEnt.set (libuser.GIDNUMBER, gidNumber)
                 cn = groupEnt.get(libuser.GROUPNAME)[0]

--Oleg


At 23/01/2008 Al Russell wrote:
> I have recently done a clean install of SL-5.1 (workstation).
> Everything seemed to be working fine until I tried to add additional
> users using the command line to invoke the Add-Users GUI. When Add
> user button was clicked the GUI grayed out and froze. I had to ^C out.
> A portion of the dialog follows.
> 
> [root@localhost etc]# which system-config-users
> /usr/bin/system-config-users
> [root@localhost etc]# system-config-users
> Traceback (most recent call last):
>   File "/usr/share/system-config-users/userWindow.py", line 354, in
> on_userWin_ok_button_clicked
>     groupEnt.set (libuser.GROUPNAME, groupName)
> NameError: global name 'groupName' is not defined
> [root@localhost etc]# 
> 
> The additional user was not added. Does anyone have any suggestions
> where I should be looking to fix the problem?
> 
> Previously I have had SL-4.x and SL-5.0 installed on the system and no
> problems were encountered.
> 
> Thanks,
> Al
>