I've spotted this in my Latitude settings:

Account settings -> Authorizing applications & sites -> You have granted the following services access to your Google Account: LatitudeUpdater -> More info -> You haven't given <<NUMBER>>.apps.googleusercontent.com any permission to access your Latitude location information.

I've run /opt/linfati.com/bin/LatitudeUpdaterDaemon in a shell and noticed the following problems:

* GoogleLatitude::onRequestReady "{"error":{"errors":[{"domain":"global","reason":"insufficientPermissio ns","message":"The user is not opted in to Google Latitude."}],"code":403,"message":"The user is not opted in to Google Latitude."}}"


* GoogleLatitude::sendCurrentLocation
json_location "{"data": {"kind":"latitude#location","latitude":<<LATITUDE> >,"longitude":<<LONGITUDE>>,"accuracy":<<ACCURACY> >}}"
("Authorization", "Content-Type")
"OAuth oauth_signature_method="HMAC-SHA1", oauth_consumer_key="<<NUMBER>>.apps.googleusercont ent.com", oauth_version="1.0", oauth_timestamp="<<NUMBER>>", oauth_nonce="<<NUMBER>>", oauth_token="<<TOKEN>>", oauth_signature="<<SIGNATURE>>""
"application/json"
* GoogleLatitude::onRequestReady ""
* GoogleLatitude::onAuthorizedRequestDone
* GoogleLatitude::onRequestReady "{"error":{"errors":[{"domain":"global","reason":"backendError","messag e":"Backend Error"}],"code":503,"message":"Backend Error"}}"

Hope this helps...