1. Have you imported your python module on __init__,py where your custom class are declared?
2. Have you called your class after the class declaration?
3. Have you imported the crm module on __openerp__.py file?

Example:

my_module.py file:

 class my_crm_lead(base_stage, format_address, osv.osv):
    _inherit='crm.lead'
    def create(self, cr, uid, vals, context=None):
         if context is None:
            context = {}
         create_context = dict(context)
         return super(crm_lead, self).create(cr, uid, vals, context=create_context)

my_crm_lead() #call the class it's required

__init__.py file:

import my_module

__openerp__.py file:

{
   'name': 'My CRM',
   'version': '1.0',
   'category': '...',
   'description':"...",
   'depends': ['crm'],
   'installable': True,
}