Postfix Postscreen: how to use postscreen for smtp and smtps both

I'm trying to get postscreen work. I've followed the man page and it's already running correctly for smtp.

But it I want to use it for smtps as well (adding the same line as smtp in master.cf but with smtps) i receive failure messages in syslog like:

postfix/postscreen[8851]: fatal:
btree:/var/lib/postfix/postscreen_cache: unable to get exclusive lock:
Resource temporarily unavailable

Some say that postscreen can only run once; that's ok. But can I use the same postscreen session for both smtp and smtps? If not, how to enable postscreen for smtps as well?

Any help would be apprecieted!

The parts of the configs:

main.cf postscreen_access_list = permit_mynetworks, cidr:/etc/postfix/postscreen_access.cidr

postscreen_dnsbl_threshold = 8
postscreen_dnsbl_sites = dnsbl.ahbl.org*3 dnsbl.njabl.org*3 dnsbl.sorbs.net*3 pbl.spamhaus.org*3 cbl.abuseat.org*3 bl.spamcannibal.org*3 nsbl.inps.de*3 spamrbl.imp.ch*3
postscreen_dnsbl_action = enforce
postscreen_greet_action = enforce

master.cf (full)

smtpd     pass  -       -       n       -       -       smtpd
smtp      inet  n       -       n       -       1       postscreen
tlsproxy  unix  -       -       n       -       0       tlsproxy
dnsblog   unix  -       -       n       -       0       dnsblog

### the problematic line ###
smtps     inet  n       -       -       -       -       smtpd

pickup    fifo  n       -       -       60      1       pickup
cleanup   unix  n       -       -       -       0       cleanup
qmgr      fifo  n       -       n       300     1       qmgr
tlsmgr    unix  -       -       -       1000?   1       tlsmgr
rewrite   unix  -       -       -       -       -       trivial-rewrite
bounce    unix  -       -       -       -       0       bounce
defer     unix  -       -       -       -       0       bounce
trace     unix  -       -       -       -       0       bounce
verify    unix  -       -       -       -       1       verify
flush     unix  n       -       -       1000?   0       flush
proxymap  unix  -       -       n       -       -       proxymap
proxywrite unix -       -       n       -       1       proxymap
smtp      unix  -       -       -       -       -       smtp
relay     unix  -       -       -       -       -       smtp
showq     unix  n       -       -       -       -       showq
error     unix  -       -       -       -       -       error
retry     unix  -       -       -       -       -       error
discard   unix  -       -       -       -       -       discard
local     unix  -       n       n       -       -       local
virtual   unix  -       n       n       -       -       virtual
lmtp      unix  -       -       -       -       -       lmtp
anvil     unix  -       -       -       -       1       anvil
scache    unix  -       -       -       -       1       scache

dovecot   unix  -       n       n        -      -       pipe
  flags=DRhu user=virtuser:virtuser argv=/usr/bin/spamc -e /usr/lib/dovecot/deliver -d ${recipient} -f {sender}