I am trying to install a custom module which in inherits account.invoice.tax

but  i keep getting this error :

'You may need to add a dependency on the parent class\' module.' % (name, parent)) TypeError: The model "account.invoice.tax" specifies an unexisting parent class "account.invoice.tax " You may need to add a dependency on the parent class' module.

__openerp__.py :
    "name" : "Camden Market Managers",
    "version" : "1.0",
    "author" : "Zeraxis Ltd",
    "category" : "Tools",
    "website": "http://www.zeraxis.com",
    "description": """Custom module to extend features for market managers """,
    "depends" : ["base" , "report" , "analytic" , "account" , 'edi' , 'product'],
    "data" : [
              #"cm_rental_contracts_view.xml",
              "cm_account_analytic_account_view.xml",
              "report/cm_report_retail_contracts.xml",
              "report/cm_report_storage_contracts.xml",
              "report/cm_report_food_contracts.xml",
                  "security/market_managers_security.xml",
              "security/ir.model.access.csv",
              "views/report_retailcontracts.xml",
              "views/report_foodcontracts.xml",
              "views/report_storagecontracts.xml",
                  "views/cm_market_managers_view.xml"
                  
     ],
    "demo": [],
    "active": False,
    "installable": True
}

example of module.py :

class cm_account_tax_inherit(osv.osv):
    _name = "account.invoice.tax"
    _inherit = "account.invoice.tax "
    _columns = {
      
    }

I thought by me adding the account in my depends would have solve the problem but it hasnt any ideas ?