One of my websites had begun to use Amazon ELB for load balancing.
After that, I have experienced the issue that I can't do +1 at the site.
As long as I see the webmaster tools, the +1 audience has stopped its increase since that time.
In addition, the site has issues too on several Google's services such as Google Wireless Transcoder, Google Translation and so on.
They report that it can't access to the site.
In my observation, some of Google servers have incorrect DNS caching, so thus the services couldn't access to the site, because the IP address is no longer pointing the original server.
The DNS of Amazon ELB has TLS of 60 seconds. Google's DNS caching should expire within that period.
** See Also **
** Update **
It's turned out that Google+ itself too causes this problem.
