Error in mail.log, ispcp-arpl-msgr dies with status 13 ?

[uwe]

Hello, i get these messages in my mail.log:

Oct 25 08:33:23 earth postfix/pipe[16965]: ADBB61094E6: to=<user@ispcp-arpl.
somedomain.com>, orig_to=<user@somedomain.com>, relay=ispcp-arpl,
delay=1.7, delays=0.94/0.12/0/0.67, dsn=5.3.0, status=bounced (Command died with status 13: "/var/www/ispcp/engine/messager/ispcp-arpl-msgr". Command output: Can't redirect stdout at /var/www/ispcp/engine/messager/ispcp-arpl-msgr line 555.
)

line 555 in /var/www/ispcp/engine/messager/isp-arpl-msgr is:

open(STDOUT, ">", $main::ispcp_arpl_msgr_stdout) || die "Can't redirect stdout";

and $main:ispcp_arpl_msgr_stdout is "/var/log/ispcp/ispcp-arpl-msgr/ispcp-arpl-msgr.stderr";

i tried adding write permission to all and it fixes the problem, my question is , who should be the owner ? postfix ?