Here is what is happening.
I believe Google spiders can access the forum. I have checked through Webmaster Tools.
But Google +1 button is not working.
Not working even from Google search result pages.
Also noticed that if I try to share a link through Google Plus, Google tells me that the URL is unreachable:
But if I try to share a static HTML file, it is accessed just fine:
What I have checked...
reverted all modified templates.
checked the htaccess file.
disabled nice URLs. did not change the behavior.
even tried renaming the htaccess file... no use.
everything seems to be ok. but i am just failing to resolve this problem.
Just noticed that sharing link of this forum too is not working on Google Plus:
And clicking the Google +1 button is also not working below.