This is an upstream ​Twisted bug, I have created a ticket there: ​ticket 5496

Not much we can do at this end, as it just looks to us like the key is invalid... Maybe we ought to show an alert message in this case?
See also: #190, since MS Windows does not have support for pageant, we need a way to load the keys ourselves!

Also somewhat reminiscent of #160

On Unices we can just grab the location of the SSH_AUTH_SOCK environment variable and connect to it.

On Windows, no idea.

I had an xterm, a "git gui" and a gvim connected via winswitch from a remote machine. After going away and coming back, only one of the sessions (xterm) could be resumed; new sessions (xterm again) could be started.

Here's a filtered strace on winswitch_server when trying a reconnect:

write(2, "/usr/lib/pymodules/python2.6/gtk-2.0/gtk/__init__.py:57: GtkWarning: could not open display\n  warnings.warn(str(e), _gtk.Warning)\n", 130) = 130
write(2, "/usr/lib/xpra/xpra/xposix/gui.py:15: GtkWarning: IA__gdk_display_get_name: assertion `GDK_IS_DISPLAY (display)' failed\n  _display = gtk.gdk.get_display()\n", 154) = 154
write(2, "Traceback (most recent call last):\n", 35) = 35
write(2, "  File \"/usr/bin/xpra\", line 7, in <module>\n", 44) = 44
write(2, "    ", 4) = 4
write(2, "xpra.scripts.main.main(__file__, sys.argv)\n", 43) = 43
write(2, "  File \"/usr/lib/xpra/xpra/scripts/main.py\", line 232, in main\n", 63) = 63
write(2, "    ", 4) = 4
write(2, "run_client(parser, options, args, mode)\n", 40) = 40
write(2, "  File \"/usr/lib/xpra/xpra/scripts/main.py\", line 367, in run_client\n", 69) = 69
write(2, "    ", 4) = 4
write(2, "from xpra.client import XpraClient\n", 35) = 35
write(2, "  File \"/usr/lib/xpra/xpra/client.py\", line 25, in <module>\n", 60) = 60
write(2, "    ", 4) = 4
write(2, "from xpra.platform.gui import ClientExtras\n", 43) = 43
write(2, "  File \"/usr/lib/xpra/xpra/platform/gui.py\", line 16, in <module>\n", 66) = 66
write(2, "    ", 4) = 4
write(2, "from xpra.xposix.gui import *\n", 30) = 30
write(2, "  File \"/usr/lib/xpra/xpra/xposix/gui.py\", line 16, in <module>\n", 64) = 64
write(2, "    ", 4) = 4
write(2, "assert _display, \"cannot open the display with GTK, is DISPLAY set?\"\n", 69) = 69
write(2, "AssertionError", 14) = 14
write(2, ": ", 2) = 2
write(2, "cannot open the display with GTK, is DISPLAY set?", 49) = 49
write(2, "\n", 1) = 1