This has been reported to Ubuntu Launchpad as:
https://launchpad.net/bugs/540163

Sometimes when I plugin an encrypted disk and enter the password, I get the error "mount: special device /dev/dm-X does not exist .".

This might be related to bug #527738 but it is clearly a different symptom. Anyone else with this? Any ideas on how to debug. dmesg / syslog don't help much.

Regards, Lars

ProblemType: Bug
Architecture: amd64
Date: Wed Mar 17 11:47:09 2010
DistroRelease: Ubuntu 9.10
InstallationMedia: Xubuntu 9.10 "Karmic Koala" - Release amd64 (20091027)
NonfreeKernelModules: fglrx
Package: thunar-volman 0.3.80-2ubuntu1
ProcEnviron:
 PATH=(custom, user)
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-20.57-generic
SourcePackage: thunar-volman
Uname: Linux 2.6.31-20-generic x86_64
 CancelOk

The following error is found in ~/.xsession-error log referenced:

(update-notifier:2722): libgdu-WARNING **: Couldn't call GetAll() to get properties for /org/freedesktop/DeviceKit/Disks/devices/dm_2d4: Method "GetAll" with signature "s" on interface "org.freedesktop.DBus.Properties" doesn't exist
(update-notifier:2722): libgdu-WARNING **: No device to remove for remove /org/freedesktop/DeviceKit/Disks/devices/dm_2d4

log available - http://launchpadlibrarian.net/41112677/XsessionErrors.txt