send by email error

I get this error every time i try to send purchase orders and sales order by email

OpenERP Server Error
Client Traceback (most recent call last):
  File "/opt/openerpv7/web/addons/web/http.py", line 195, in dispatch
    response["result"] = method(self, **self.params)
  File "/opt/openerpv7/web/addons/web/controllers/main.py", line 1078, in call_kw
    return self._call_kw(req, model, method, args, kwargs)
  File "/opt/openerpv7/web/addons/web/controllers/main.py", line 1070, in _call_kw
    return getattr(req.session.model(model), method)(*args, **kwargs)
  File "/opt/openerpv7/web/addons/web/session.py", line 43, in proxy
    result = self.proxy.execute_kw(self.session._db, self.session._uid, self.session._password, self.model, method, args, kw)
  File "/opt/openerpv7/web/addons/web/session.py", line 31, in proxy_method
    result = self.session.send(self.service_name, method, *args)
  File "/opt/openerpv7/web/addons/web/session.py", line 104, in send
    raise xmlrpclib.Fault(openerp.tools.exception_to_unicode(e), formatted_info)

Server Traceback (most recent call last):
  File "/opt/openerpv7/web/addons/web/session.py", line 90, in send
    return openerp.netsvc.dispatch_rpc(service_name, method, args)
  File "/opt/openerpv7/server/openerp/netsvc.py", line 289, in dispatch_rpc
    result = ExportService.getService(service_name).dispatch(method, params)
  File "/opt/openerpv7/server/openerp/service/web_services.py", line 614, in dispatch
    res = fn(db, uid, *params)
  File "/opt/openerpv7/server/openerp/osv/osv.py", line 169, in execute_kw
    return self.execute(db, uid, obj, method, *args, **kw or {})
  File "/opt/openerpv7/server/openerp/osv/osv.py", line 123, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "/opt/openerpv7/server/openerp/osv/osv.py", line 179, in execute
    res = self.execute_cr(cr, uid, obj, method, *args, **kw)
  File "/opt/openerpv7/server/openerp/osv/osv.py", line 166, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "/opt/openerpv7/addons/email_template/wizard/mail_compose_message.py", line 85, in onchange_template_id
    values['attachment_ids'].append(ir_attach_obj.create(cr, uid, data_attach, context=context))
  File "/opt/openerpv7/addons/document/document.py", line 121, in create
    vals['file_type'], vals['index_content'] = self._index(cr, uid, vals['datas'].decode('base64'), vals.get('datas_fname', False), None)
  File "/opt/openerpv7/addons/document/document.py", line 132, in _index
    mime, icont = cntIndex.doIndex(data, datas_fname, file_type or None, None)
TypeError: 'NoneType' object is not iterable