[sr-dev] MySQL - driver error on query: Commands out of sync; you can't run this command now

Hello, I installed and run Kamailio, it run pretty stabil for a while with a few phone registered, but recently encountered a mysql error, once a while, kamailio report following error: /usr/local/sbin/kamailio[11693]: INFO: <script>: route[AUTH] /usr/local/sbin/kamailio[11693]: ERROR: db_mysql [km_dbase.c:117]: driver error on query: Commands out of sync; you can't run this command now /usr/local/sbin/kamailio[11693]: ERROR: <core> [db_query.c:101]: error while submitting query /usr/local/sbin/kamailio[11693]: ERROR: auth_db [authorize.c:102]: failed to query database the freq of these error getting increase once we introduce more clients. Try to google about this type of error, but found a mix suggestion without clear answer/suggestion. Any pointer/suggestion on how to troubleshoot? Thanks in advance for you help. ======== i'm running : Server: kamailio (3.0.3 (i386/linux)) a22dc9 Mysql: 5.0.77 CentOS 5.5