[squid-users] squidaio_queue_request : warning - queue congestion

hi squid user
i use squid 3.1.11 with 3 cach_dir aufs 5000 MB and 4GB ram for computer
and 512 MB for squid in cache_mem
some times i gate this message in my cache.log
please can you tell me what is the problem

 clientProcessRequest: Invalid Request
2012/02/01 08:18:01| clientProcessRequest: Invalid Request
2012/02/01 08:18:15| clientProcessRequest: Invalid Request
2012/02/01 08:29:32| clientProcessRequest: Invalid Request
2012/02/01 08:36:32| clientProcessRequest: Invalid Request
2012/02/01 08:40:34| clientProcessRequest: Invalid Request
2012/02/01 08:57:38| squidaio_queue_request: WARNING - Queue congestion
2012/02/01 09:10:44| clientProcessRequest: Invalid Request
2012/02/01 09:18:32| clientProcessRequest: Invalid Request
2012/02/01 10:10:45| clientProcessRequest: Invalid Request
2012/02/01 10:11:34| clientProcessRequest: Invalid Request
2012/02/01 10:20:04| clientProcessRequest: Invalid Request
2012/02/01 11:11:01| clientProcessRequest: Invalid Request
2012/02/01 11:11:07| clientProcessRequest: Invalid Request
:
Received on Wed Feb 01 2012 - 18:18:51 MST