[Serusers] EXEC error on syslog

Hello, when I set : log_stderror = NO (with log_stderror = Yes, where are the logs????? ) when I use, log(1,"registration successful!!!"); the message "registration successful!!!" is write on the syslog. But if I use an exec_msg command, the syslog write an error : Oct 13 16:09:02 sip2 /usr/sbin/ser[30167]: INFO: SIGCHLD received: we do not worry about grand-children Oct 13 16:09:02 sip2 /usr/sbin/ser[30167]: ERROR: exec_msg: cmd echo $SIP_SRCIP >> /tmp/testLOG.txt; failed. exit_status=-1, errno=32: Broken pipe But in testLOG.txt, i have the good information !!! Why i have this error. Thanks a lot Best regards Nicolas RUIZ