res_odbc problems

I am develeping a SIP Phone system.
Asterisk 1.4+ unixodb +MS SQL realtime
users management;call rates;pre-paid;etc
but I found sometimes,when I invite
Asterisk will display '403’
and below:
Feb 16 14:51:50 WARNING[13534] res_config_odbc.c: SQL Prepare failed![proc_INVITE_Auth_new ‘68681006’,‘9991000’,7,‘SIP’] and Error in PREPARE -1
Feb 16 14:51:50 WARNING[13534] res_config_odbc.c: The driver reported the following diagnostics whilst running

So I type ‘odbc show’ in CLI,and astersik start to re-connect MSSQL by UNIXODBC

Any help?