Site is temporarily unavailable

I am, on occasion getting a message that the site is temporarily unavailable.

It is particularly annoying that it seems to happen only after I have composed a reply to a forum post.
More so when it is a long reply since I lose all I have entered.

Clearly, the site is available since I can get to the home page always right after.

Is there a reason?
It seems to be more prevalent since I have switched to IE10.
 
It happens to me sometimes then when I double check, I find it put the post up but still displayed that message. It's wise, though, until it's fixed, to clipboard everything you write before clicking to post - just in case.