all servers are running and nginx has the following error log every once in a while.

2010/07/27 08:37:57 [error] 1948#0: *429632943 connect() failed (111: Connection refused) while connecting to upstream, client: 125.45.229.167, server: xx.xxx.xxx, request: "GET xxxx HTTP/1.1", upstream: "server://xx.xxx.xxx.xxx:xxxxx", host: "xxx.xxx.xxx", referrer: "xxx"


Is the listen queue full ?what causes the above problem?
thx