3
Let me ask a couple of questions.
How much traffic does your site get per day?
Has that number increased lately? You might have to check your hosting provider logs if they keep that information for you.
I've taken a look at this, and there seem to be a few things about that way we are using stopforumspam.com that should be fixed. It is possible that if you have enough activity that your site IP gets flagged by stopforumspam.com and it stops sending the information. If it returned an error message instead of the formatted response we expect, that would cause your error.
It appears that we are checking every post, and we are not doing local caching
If a site gets a lot of post traffic it could easily get flagged with the current setup. This article is specifically about a Drupal mod, but the issue sounds similar:
http://www.stopforumspam.com/forum/viewtopic.php?id=5136This might take a little while to solve. Does anyone else have similar issues?