"Access denied" despite of being a public post

@helpers

Some of the articles I write doen't seem to get delivered fully to where ever it is they should be delivered to. Sometimes there is a little paper plane appearing (e.g. in the headline area of this article: opensocial.at/display/59c238fc…) which says "Die Zustellung an remote server ist fast erledigt 176/177" meaning something like "Delivery to remote server is almost done 176/177"

It seems as if people often get errors (Access Denied) even though the article is public.

Is there something I can do about it? Is it a bug? Did I configure something wrongly?