Having the same problem again today. Same error message:
The connection to www.birdforum.net
was interrupted while the page was loading.
The page you are trying to view cannot be shown because the authenticity of the received data could not be verified.
Please contact the web site owners to inform them of this problem.
There's a noticeable delay while my machine tries to establish a connection with the Birdforum server. I guess I'll leave it at uploading just the one photo today and I'll try again tomorrow. Restarting the browser did not help.
It definitely seems to be a server-side thing.