Special caracters in CRM stages

If you uses stages name with special caracters you will not be able to add them to any opportunities
  File "/usr/lib/python2.5/site-packages/openerp-server/netsvc.py", line 431, in dispatch
    result = ExportService.getService(service_name).dispatch(method, auth, params)
  File "/usr/lib/python2.5/site-packages/openerp-server/service/web_services.py", line 589, in dispatch
    res = fn(db, uid, *params)
  File "/usr/lib/python2.5/site-packages/openerp-server/osv/osv.py", line 57, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "/usr/lib/python2.5/site-packages/openerp-server/osv/osv.py", line 135, in execute
    res = pool.execute_cr(cr, uid, obj, method, *args, **kw)
  File "/usr/lib/python2.5/site-packages/openerp-server/osv/osv.py", line 125, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "/usr/lib/python2.5/site-packages/openerp-server/osv/orm.py", line 1712, in fields_view_get
    xarch, xfields = self.__view_look_dom_arch(cr, user, result['arch'], view_id, context=context)
  File "/usr/lib/python2.5/site-packages/openerp-server/osv/orm.py", line 1374, in __view_look_dom_arch
    fields_def = self.__view_look_dom(cr, user, node, view_id, context=context)
  File "/usr/lib/python2.5/site-packages/openerp-server/osv/orm.py", line 1361, in __view_look_dom
    node.set('string', trans)
  File "lxml.etree.pyx", line 639, in lxml.etree._Element.set (src/lxml/lxml.etree.c:8269)
  File "apihelpers.pxi", line 416, in lxml.etree._setAttributeValue (src/lxml/lxml.etree.c:29149)
  File "apihelpers.pxi", line 1136, in lxml.etree._utf8 (src/lxml/lxml.etree.c:34600)
ValueError: All strings must be XML compatible: Unicode or ASCII, no NULL bytes