[Dovecot] Error: net_connect(/var/run/dovecot/auth-master) failed: Resource temporarily unavailable

I'm using deliver (1.0.5) with Postfix (2.1.6). I made a test for a few minutes in a moderated busy server. While most mails was delivered, a lot of them failed with this error:

deliver(userfoo): Oct 15 09:58:31 Error: net_connect(/var/run/dovecot/auth-master) failed: Resource temporarily unavailable

Sounds to me something like not enough auth-master to answer every concurrent deliver.

Any hint?

Regards, maykel

PD: If there any other info I could give let me know.