Hi there. This happened last night after I was tweaking the number of FastCGI processes. I changed it from four backends to one. Then Lighttpd believed the backend was overloaded:

2010-03-01 07:16:21: (mod_fastcgi.c.2926) backend is overloaded; we'll disable it for 2 seconds and send the request to another backend instead: reconnects: 0 load: 131 2010-03-01 07:16:24: (mod_fastcgi.c.3569) all handlers for /haskell-json.fcgi on haskell-json.fcgi are down.

I doubt there were 131 requests to the FastCGI process at the same time but I'll have to seek more information about it. http://redmine.lighttpd.net/issues/1825

For now I've set it back to four backends as that never had this problem.