This was mentioned in #198 but it seems like it was overlooked.

NXAGENT - Version 3.5.0

Copyright (C) 2001, 2011 NoMachine.
See http://www.nomachine.com/ for more information.

Info: Agent running with pid '8227'.
Session: Starting session at 'Wed Oct  3 00:44:12 2012'.
Error: Aborting session with 'Unable to open display 'nx/nx,options=/home/me/.winswitch/server/sessions/72/nx_options.txt:72''.
Session: Aborting session at 'Wed Oct  3 00:44:12 2012'.
Session: Session aborted at 'Wed Oct  3 00:44:12 2012'.

Why is all that extra stuff being sent to NX for the display, instead of it just being ":72"?

winswitch:
  Installed: 0.12.16-4
  Candidate: 0.12.16-4
  Version table:
 *** 0.12.16-4 0
        500 http://winswitch.org/ precise/main i386 Packages
        100 /var/lib/dpkg/status

I use these versions:

[eric@pc ~]$ pacman -Q winswitch
winswitch 0.12.16-1
[eric@pc ~]$ pacman -Q xpra-winswitch
xpra-winswitch 0.6.0-1

And here are the errors... I can't really distinguish between 'serious' errors , and 'non-important' errors

I can do some more tests, just tell me...

[eric@pc ~]$ winswitch_client 
[DD] 2012/21/09 01:33:01 main_loop.loop_init(False)
[II] 2012/21/09 01:33:01 main_loop.loop_init(False) twisted version 12.1.0
[II] 2012/21/09 01:33:01 globals os.uname=('Linux', 'pc', '3.5.3-1-ARCH', '#1 SMP PREEMPT Sun Aug 26 09:14:51 CEST 2012', 'x86_64')
[II] 2012/21/09 01:33:01 globals python package info: __version__=0.12.16
[II] 2012/21/09 01:33:01 globals version=0.12.16 (svn revision unknown - unknown local modifications), built on pc by eric, 2012-09-21, release_build=True
[II] 2012/21/09 01:33:01 globals uid=1000, username=eric, name=eric, hostname=pc, locale=en_US, argv=[/usr/bin/winswitch_client]
[II] 2012/21/09 01:33:01 globals Python version 2.7.3 (default, Apr 24 2012, 00:00:54) [GCC 4.7.0 20120414 (prerelease)]

** (process:20193): WARNING **: Trying to register gtype 'GMountMountFlags' as enum when in fact it is of type 'GFlags'

** (process:20193): WARNING **: Trying to register gtype 'GDriveStartFlags' as enum when in fact it is of type 'GFlags'

** (process:20193): WARNING **: Trying to register gtype 'GSocketMsgFlags' as enum when in fact it is of type 'GFlags'
[II] 2012/21/09 01:33:01 process_util.<module>() using twisted ProcessProtocol=winswitch.twisted.HiddenSpawnedProcess.HiddenSpawnedProcess
[EE] 2012/21/09 01:33:01 distro_packaging_util.get_distro_helper() failed to load dbus packagekit: org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.PackageKit was not provided by any .service files
Traceback (most recent call last):
  File "/usr/bin/winswitch_client", line 5, in <module>
    winswitch.client.client_wrapper.main()
  File "/usr/lib/python2.7/site-packages/winswitch/client/client_wrapper.py", line 52, in main
    from winswitch.client.client import main
  File "/usr/lib/python2.7/site-packages/winswitch/client/client.py", line 14, in <module>
    from winswitch.client.client_base import ClientBase
  File "/usr/lib/python2.7/site-packages/winswitch/client/client_base.py", line 28, in <module>
    from winswitch.objects.server_config import ServerConfig
  File "/usr/lib/python2.7/site-packages/winswitch/objects/server_config.py", line 14, in <module>
    from winswitch.objects.server_base import ServerBase
  File "/usr/lib/python2.7/site-packages/winswitch/objects/server_base.py", line 27, in <module>
    from winswitch.util.commands_util import SEAMLESSRDP_COMMAND
  File "/usr/lib/python2.7/site-packages/winswitch/util/commands_util.py", line 70, in <module>
    dh = get_distro_helper()
  File "/usr/lib/python2.7/site-packages/winswitch/util/distro_packaging_util.py", line 141, in get_distro_helper
    installer(XPRA_TYPE, "xpra")
TypeError: 'NoneType' object is not callable

xpra hasn't been working the last few updates.
Checked the server log, and it showed:

[EE] 2012/10/09 19:00:14 WinSwitchServer.assign_virt_utils() failed to load xpra, make sure it is installed: No module named xpra.dotxpra

Fixed that with sudo ln -s /usr/lib/xpra /usr/lib/pyshared/python2.7/ but I still can't start an xpra session.
Server:

[DD] 2012/10/09 19:12:50 WinSwitchClientChannel.start_session(afd2118e252a679a88ea6e030680402d,xpra,,read_only=False;encoding="";,None) options={'read_only': 'False', 'encoding': '""'}
[II] 2012/10/09 19:12:50 WinSwitchClientChannel.start_session(afd2118e252a679a88ea6e030680402d,xpra,,read_only=False;encoding="";) command=Command(LXTerminal: lxterminal), user=User(Administrator : f629f85ae9424587bea966f155801421)
[II] 2012/10/09 19:12:50 WinSwitchServer.start_session(User(Administrator : f629f85ae9424587bea966f155801421),xpra,Command(LXTerminal: lxterminal),,{'read_only': 'False', 'encoding': '""'},None)
[DD] 2012/10/09 19:12:50 WinSwitchServer.real_start_session(User(Administrator : f629f85ae9424587bea966f155801421),xpra,Command(LXTerminal: lxterminal),,{'read_only': 'False', 'encoding': '""'},None)

Client:

[II] 2012/10/09 19:12:03 WinSwitchApplet.do_start_session(ServerConfig(hostname.net:346729663014),Command(LXTerminal: lxterminal),xpra,None,None,False)
[II] 2012/10/09 19:12:03 WinSwitchApplet.attention(Starting LXTerminal,None)
[II] 2012/10/09 19:12:03 ServerLineConnection.do_message(f629f85ae9424587bea966f155801421,Cannot start session,You have requested an xpra session but this server does not support it,)
[II] 2012/10/09 19:12:03 WinSwitchApplet.do_notify(Cannot start session,You have requested an xpra session but this server does not support it,None,None,info,ServerConfig(hostname.net:346729663014),)
[II] 2012/10/09 19:12:03 win32_balloon.notify(5112608,Cannot start session,You have requested an xpra session but this server does not support it\nClick to Edit Server Configuration,5)
[II] 2012/10/09 19:12:03 WinSwitchApplet.attention(Cannot start session,None)
[II] 2012/10/09 19:12:03 Win32Tray.MyWndProc(5112608,1044,0,1026) NIN_BALLOONSHOW

This was with: Server: Ubuntu 12.04 64bit, Client: Windows 7 64bit Both are running v0.12.16

$ dpkg -l winswitch xpra
ii  winswitch                                  0.12.16-1
ii  xpra                                       0.6.0-5