trytond crashed with ImportError in /usr/lib/python2.7/dist-packages/psycopg2/__init__.py: can't import mx.DateTime module

after boot

ProblemType: Crash
DistroRelease: Ubuntu 11.10
Package: tryton-server 2.0.1-1ubuntu1
ProcVersionSignature: Ubuntu 3.0.0-7.9-generic 3.0.0
Uname: Linux 3.0.0-7-generic x86_64
Architecture: amd64
Date: Wed Jul 27 00:09:32 2011
ExecutablePath: /usr/bin/trytond
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Alpha amd64 (20110705.1)
InterpreterPath: /usr/bin/python2.7
PackageArchitecture: all
ProcCmdline: /usr/bin/python /usr/bin/trytond --config=/etc/trytond.conf --logfile=/var/log/tryton/trytond.log
ProcEnviron:
 PATH=(custom, no user)
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
PythonArgs: ['/usr/bin/trytond', '--config=/etc/trytond.conf', '--logfile=/var/log/tryton/trytond.log']
SourcePackage: tryton-server
Title: trytond crashed with ImportError in /usr/lib/python2.7/dist-packages/psycopg2/__init__.py: can't import mx.DateTime module
UpgradeStatus: No upgrade log present (probably fresh install)
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