My log file has a large number of exceptions like the one below; what could be the cause?

It happens every time a remote user first connects to my server URL, before any attempt to login.

I expect I have an incomplete or incorrect configuration of portal.

I have installed and configured:

• auth_signup
• auth_oauth
• auth_oauth_signup
• portal
• portal_anonymous
• web

WARNING demo_db openerp.osv.orm: 
  Access Denied by record rules for operation: read, uid: 4, model: res.partner
ERROR demo_db openerp.netsvc: Access Denied
The requested operation cannot be completed due to security restrictions. 
Please contact your system administrator.

(Document type: Partner, Operation: read)
Traceback (most recent call last):

  File "/opt/openerp/server/openerp/netsvc.py", line 293, in dispatch_rpc
    result = ExportService.getService(service_name).dispatch(method, params)

  File "/opt/openerp/server/openerp/service/web_services.py", line 618, in dispatch
    res = fn(db, uid, *params)

  File "/opt/openerp/server/openerp/osv/osv.py", line 188, in execute_kw
    return self.execute(db, uid, obj, method, *args, **kw or {})

  File "/opt/openerp/server/openerp/osv/osv.py", line 144, in wrapper
    raise except_osv(inst.name, inst.value)

except_osv: (u'Access Denied', u'The requested operation cannot be completed due to security restrictions. Please contact your system administrator.\n\n(Document type: Partner, Operation: read)')

INFO demo_db werkzeug: 186.42.57.48 - - [10/Apr/2013 11:33:26] "GET /web/binary/image?model=res.partner&field=image_small&id=3&resize=&session_id=6d483e80dd3247a5a23f52676f301286 HTTP/1.1" 200 -