Apache, Mongrel proxy issue

So I have apache set up as:

<Proxy balancer://mongrel_cluster>
  BalancerMember http://127.0.0.1:8000
  BalancerMember http://127.0.0.1:8001
  BalancerMember http://127.0.0.1:8002
  BalancerMember http://127.0.0.1:8003
</Proxy>

Every so often, I get this in the apache error_log and my site hanges:

(70014)End of file found: proxy: error reading status line from remote
server 127.0.0.1, referer:..........

OR

(70014)End of file found: proxy: error reading status line from remote
server 127.0.0.1

Any ideas?