Could it be a limit on maximum allowed open file descriptors? I have seen this log message on server with many nodes, and increasing the FD:s helped. This server now reports (for root user)
# ulimit -n
8192
# ulimit -Hn
16384
# ulimit -Sn
8192
To increase (at least on debian), see /etc/security/limits.conf and pherhaps /etc/sysctl.conf.
My limits.conf includes
root soft nofile 8192
root hard nofile 16384
Regards,
Kjell