Crash OpenERP 7 startup 'module' object has no attribute 'tools'

Hello

I have a serious problem when start OpenERP 7.0.

Server doesn't runs and log in /var/log/openerp/openerp-server.log doesn't update.

When I try to start Openerp via console says:

jsallent@IQERP:/usr/bin$ openerp-server
Traceback (most recent call last):
  File "/usr/bin/openerp-server", line 2, in <module>
    import openerp
  File "/usr/lib/pymodules/python2.7/openerp/__init__.py", line 40, in <module>
    import cli
  File "/usr/lib/pymodules/python2.7/openerp/cli/__init__.py", line 5, in <module>
    from openerp import tools
  File "/usr/lib/pymodules/python2.7/openerp/tools/__init__.py", line 26, in <module>
    from convert import *
  File "/usr/lib/pymodules/python2.7/openerp/tools/convert.py", line 49, in <module>
    import openerp.pooler as pooler
  File "/usr/lib/pymodules/python2.7/openerp/pooler.py", line 28, in <module>
    from openerp.modules.registry import RegistryManager
  File "/usr/lib/pymodules/python2.7/openerp/modules/__init__.py", line 27, in <module>
    from . import db, graph, loading, migration, module, registry
  File "/usr/lib/pymodules/python2.7/openerp/modules/graph.py", line 32, in <module>
    import openerp.osv as osv
  File "/usr/lib/pymodules/python2.7/openerp/osv/__init__.py", line 22, in <module>
    import osv
  File "/usr/lib/pymodules/python2.7/openerp/osv/osv.py", line 30, in <module>
    import orm
  File "/usr/lib/pymodules/python2.7/openerp/osv/orm.py", line 62, in <module>
    import fields
  File "/usr/lib/pymodules/python2.7/openerp/osv/fields.py", line 47, in <module>
    import openerp.tools as tools
AttributeError: 'module' object has no attribute 'tools'

Can you give some information to solve the problem?.

How could runs OpenERP with another db_name? ... I believe in the table of the database ir.module.module want to update a exist module and in ir.model.fields field is missing ???

Thanks in advance.

Juan