Odoo Server Error

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 546, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 583, in dispatch
    result = self._call_function(**self.params)
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 319, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/openerp/service/model.py", line 118, in wrapper
    return f(dbname, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 316, in checked_call
    return self.endpoint(*a, **kw)
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 812, in __call__
    return self.method(*args, **kw)
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 412, in response_wrap
    response = f(*args, **kw)
  File "/usr/lib/python2.7/dist-packages/openerp/addons/web/controllers/main.py", line 948, in call_button
    action = self._call_kw(model, method, args, {})
  File "/usr/lib/python2.7/dist-packages/openerp/addons/web/controllers/main.py", line 936, in _call_kw
    return getattr(request.registry.get(model), method)(request.cr, request.uid, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 268, in wrapper
    return old_api(self, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/openerp/addons/base/module/module.py", line 447, in button_immediate_install
    return self._button_immediate_function(cr, uid, ids, self.button_install, context=context)
  File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 268, in wrapper
    return old_api(self, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/openerp/addons/base/module/module.py", line 495, in _button_immediate_function
    registry = openerp.modules.registry.RegistryManager.new(cr.dbname, update_module=True)
  File "/usr/lib/python2.7/dist-packages/openerp/modules/registry.py", line 370, in new
    openerp.modules.load_modules(registry._db, force_demo, status, update_module)
  File "/usr/lib/python2.7/dist-packages/openerp/modules/loading.py", line 355, in load_modules
    loaded_modules, update_module)
  File "/usr/lib/python2.7/dist-packages/openerp/modules/loading.py", line 255, in load_marked_modules
    loaded, processed = load_module_graph(cr, graph, progressdict, report=report, skip_modules=loaded_modules, perform_checks=perform_checks)
  File "/usr/lib/python2.7/dist-packages/openerp/modules/loading.py", line 176, in load_module_graph
    _load_data(cr, module_name, idref, mode, kind='data')
  File "/usr/lib/python2.7/dist-packages/openerp/modules/loading.py", line 118, in _load_data
    tools.convert_file(cr, module_name, filename, idref, mode, noupdate, kind, report)
  File "/usr/lib/python2.7/dist-packages/openerp/tools/convert.py", line 897, in convert_file
    convert_xml_import(cr, module, fp, idref, mode, noupdate, report)
  File "/usr/lib/python2.7/dist-packages/openerp/tools/convert.py", line 983, in convert_xml_import
    obj.parse(doc.getroot(), mode=mode)
  File "/usr/lib/python2.7/dist-packages/openerp/tools/convert.py", line 849, in parse
    self._tags[rec.tag](self.cr, rec, n, mode=mode)
  File "/usr/lib/python2.7/dist-packages/openerp/tools/convert.py", line 759, in _tag_record
    id = self.pool['ir.model.data']._update(cr, self.uid, rec_model, self.module, res, rec_id or False, not self.isnoupdate(data_node), noupdate=self.isnoupdate(data_node), mode=self.mode, context=rec_context )
  File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 268, in wrapper
    return old_api(self, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/openerp/addons/base/ir/ir_model.py", line 1069, in _update
    res_id = model_obj.create(cr, uid, values, context=context)
  File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 268, in wrapper
    return old_api(self, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/openerp/addons/base/ir/ir_ui_view.py", line 263, in create
    context=context)
  File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 268, in wrapper
    return old_api(self, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 372, in old_api
    result = method(recs, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/openerp/models.py", line 4101, in create
    record = self.browse(self._create(old_vals))
  File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 266, in wrapper
    return new_api(self, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 508, in new_api
    result = method(self._model, cr, uid, *args, **old_kwargs)
  File "/usr/lib/python2.7/dist-packages/openerp/models.py", line 4298, in _create
    recs._validate_fields(vals)
  File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 266, in wrapper
    return new_api(self, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/openerp/models.py", line 1275, in _validate_fields
    raise ValidationError('\n'.join(errors))
ParseError: "ValidateError
Field(s) `arch` failed against a constraint: Invalid view definition" while parsing /mesaddons/bxcamion2/views/bxcamionF_views.xml:4, near
<record id="bxcamion_form" model="ir.ui.view">
     <field name="name">bxcamion.form</field>
     <field name="model">bxcamion.bxcamion</field>
     <field name="arch" type="xml">
            <form string="Fiche du vehicule">
                <field name="immatriculation"/>
                    <sheet>
                        <page id="general" name="General">
                            <group>
                                <field name="motorisation"/>
                                <field name="Date_mise_en_service"/>
                                <field name="Type_de_vehicule"/>
                                <field name="Date_d_achat"/>
                                <field name="Nombre_de_chevaux"/>
                                <field name="NSerie"/>
                                <field name="PTAC"/>
                                <field name="PaV"/>
                                <field name="PTRA"/>
                                <field name="co2"/>
                            </group>
                        </page>
                        <page id="comptabilite" name="comptabilite">
                           <group>
                                <field name="Financement"/>
                                <field name="A_Vendre"/>
                                <field name="A_detruire"/>
                                <field name="Immobilisation"/>
                           </group>
                        </page>
                        <page id="suivi" name="suivi">
                           <group>
                                <field name="der_Date_chronotachygraphe"/>
                                <field name="der_Date_VGP"/>
                                <field name="der_Date_EXTINCTEUR"/>
                                <field name="derniere_Date_agres"/>
                                <field name="pro_Date_chronotachygraphe"/>
                                <field name="Pro_Date_VGP"/>
                                <field name="Pro_Date_EXTINCTEUR"/>
                                <field name="Pro_Date_agres"/>
                            </group> 
                      </page>
                  </sheet>
            </form>
        </field>  
   </record>