[Dovecot] Resource temporarily unavailable

[Len7hir]

On very high traffic in POP3 I have flood of messages in my log:

Feb  2 16:32:17 pp4 dovecot: pop3: Error: 
net_connect_unix(/var/run/dovecot/auth-master) failed: Resource 
temporarily unavailable


What a Terrible Failure (WTF)?


Can You help me resolve this problem?
I've not found any info about auth-master problem :/

My settings:
default_process_limit = 2000
default_client_limit = 4096

service pop3-login {
     service_count = 0
     vsz_limit = 128M
     process_min_avail = 8
}


FD limit in system = 32000
8 cpu, 28GB RAM
about 50 login per second


Different Error messages I've when set service_count = 1.
Feb  2 10:21:29 pp4 dovecot: pop3-login: (5052) Disconnected: Connection 
queue full (no auth attempts)

--
Len7hir