warning "Exception in cron" in open-server.log

[Sylvain Plante]

Here is the message in open-server.log

2013-01-08 11:35:02,891 192 WARNING BEopenERP openerp.addons.base.ir.ir_cron: Exception in cron:
Traceback (most recent call last):
  File "C:\Program Files\OpenERP 7.0alpha\Server\server\openerp\addons\base\ir\ir_cron.py", line 199, in _acquire_job
  File "C:\Program Files\OpenERP 7.0alpha\Server\server\.\openerp\sql_db.py", line 162, in wrapper
  File "C:\Program Files\OpenERP 7.0alpha\Server\server\.\openerp\sql_db.py", line 227, in execute
TransactionRollbackError: could not serialize access due to concurrent update

Follow is the message in Progresql logfile

013-01-08 11:37:04 EST ERROR: could not serialize access due to concurrent update
2013-01-08 11:37:04 EST STATEMENT: SELECT *
                                        FROM ir_cron
                                        WHERE id=7
                                        FOR UPDATE NOWAIT

I am running openerp-allinone-setup-7.0alpha-20130107-000101.exe
I went through the upgrade procedure :
    openerp-server.exe -d BEopenERP -u all
with no problem.