[squid-users] auth_param

Hi,
I have this parameters in my squid.conf :

auth_param basic program /etc/squid/mysql_auth.php
auth_param basic children 5
auth_param basic realm Squid proxy-caching web server
auth_param basic credentialsttl 2 hours

but each time the same client launch IE, He is asked for Username and
Password.
Is the parameter credentialsttl 2 hours the write parameters ?

Thanks for your help,

Bernard