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

OS: Linux olloff-desktop 3.5.0-15-generic #23-Ubuntu x86_64 x86_64 x86_64 GNU/Linux
Python: 2.7.3
Winswitch: __version__=0.12.17

Error: ​http://pastebin.com/uuLLTjAP Traceback: ​http://pastebin.com/xKW3kKnw

After fresh install 0.12.16 or update to 0.12.17 I get next error:

SyntaxError: Non-ASCII character '\xc3' in file \
/usr/lib/python2.7/dist-packages/winswitch/util/xkbmap_util.py

Problem seems to be fixed by adding encoding information to xkbmap_util.py:

# -*- coding: utf-8 -*-

starting an xpra session manually and then remotely connecting to it with the winswitch cleint for Windows results in change of xpra session to use --bind-tcp=0.0.0.0:<port>, which is a "major security risk" (xpra(1)).

Reproduction steps:

In the remote host run

$ ps aux | grep winswitch # no winswitch_server running
$ ps aux | grep xpra # no xpra running
$ xpra start :666
$ ps aux | grep xpra # see the command line and PID
1000     18905  2.5  0.2 188412 21976 ?        S    21:26   0:00 /usr/bin/python /usr/bin/xpra start :666

Now run the Window Switch client for Windows and connect to that remote host using ssh tunneling. It will show an "unknown" session. You won´t even need to resume it via the tray icon, the damage is already done:

On the remote host again:

$ ps aux | grep xpra
1000     19549  0.1  0.2 213020 23404 ?        S    21:32   0:00 /usr/bin/python /usr/bin/xpra --bind-tcp=0.0.0.0:15061 --password-file=/home/ocm-admin/.winswitch/server/sessions/666/session.pass --no-daemon --no-pulseaudio --session-name=unknown start :666 --use-display

$ ps aux | grep winsw
1000     19479  0.1  0.1 101708 15536 ?        Ss   21:31   0:00 /usr/bin/python /usr/bin/winswitch_stdio_socket
1000     19485  0.2  0.0      0     0 ?        Z    21:32   0:00 [winswitch_serve] <defunct>
1000     19533  0.2  0.3 323548 29688 ?        S    21:32   0:00 /usr/bin/python /usr/bin/winswitch_server --daemon
1000     19549  0.1  0.2 213020 23404 ?        S    21:32   0:00 /usr/bin/python /usr/bin/xpra --bind-tcp=0.0.0.0:15061 --password-file=/home/ocm-admin/.winswitch/server/sessions/666/session.pass --no-daemon --no-pulseaudio --session-name=unknown start :666 --use-display

$ netstat --inet -nlp 2>/dev/null | grep 19549
tcp        0      0 0.0.0.0:15061           0.0.0.0:*               LISTEN      19549/python

So there you are, apparently winswitch_server restarted xpra, see the different PIDs, and now it is listening on all IPs. Found no documentation about this, just stumbled upon it. No obvious way to change it in any config files. Plus this should never be the default behaviour!

For some more info, I am using Debian squeeze/stable and have installed from the official winswitch.org repository.

$ cat /etc/debian_version
6.0.5
$ apt-cache policy winswitch xpra
winswitch:
  Installiert: 0.12.14-1
  Kandidat:    0.12.14-1
  Versionstabelle:
 *** 0.12.14-1 0
        990 http://winswitch.org/ squeeze/main amd64 Packages
        100 /var/lib/dpkg/status
xpra:
  Installiert: 0.3.2-2
  Kandidat:    0.3.2-2
  Versionstabelle:
 *** 0.3.2-2 0
        990 http://winswitch.org/ squeeze/main amd64 Packages
        100 /var/lib/dpkg/status
$ winswitch_server --version
winswitch version 0.12.14
Release Build
Built on winswitch.org by root on the 2012-06-04
SVN revision unknown with unknown local modifications
$ xpra --version
xpra v0.3.2

I did not change any config files on the remote host.

The windows client version is: Window Switch 0.12.14 Built on xp-pro by XP_Pro. 2012-06-04 (release build) (svn revision 4908 with 0 local changes)

if the client version matters at all, this should clearly be changed on the server.