I dont know what that error means, but default webserver and TCP stack
options may not be helping. I investigated a Centos box with resources
issues a while back. It had many thousands of sockets in TIME_WAIT state.

IIRC i reduced /proc/sys/net/ipv4/tcp_fin_timeout from 60 to 15, and
enabled pipelining on the webserver, along with a few other webserver
tweaks.

First quick check if it happens again: netstat -an | grep -ci wait
If it returns a five figure number then the above would be worth a look.