Squid cannot send UDP messages to syslog server

I'm migrating my old Squid (2.7 in Debian 7.8 to 3.1 in CentOS 6.6)

I need to send logs to a syslog server located into another machine

I added the following config to the new server

logformat S2combined %ts.%03tu %6tr %>a %Ss/%03Hs %<st %rm %ru %[un %Sh/%<A %mt "%{Referer}>h" "%{User-Agent}>h"
access_log /var/log/squid/access.log S2combined
access_log udp://192.168.4.63:514 S2combined

This config is working fine in old server, but in the new one, Squid won't start.

I ran squid with the -d 10 option, and it shows me this in stdout:

FATAL: Cannot open 'udp://192.168.4.63:514' for writing.
    The parent directory must be writeable by the
    user 'squid', which is the cache_effective_user
    set in squid.conf.

Do anyone have any clue? I had been checking squid cache configuration reference for squid 3.1 and this config seems to be OK

Thanks in advance