do you have the php mysql module installed? you can make a phpinfo() page in the roundcube directory to check.
Thanks John,
Yep, sorry for the delayed reply, I have been away from working on my server...
I created the phpinfo() page as you suggested and I have:
mysql
MySQL Support enabled
Active Persistent Links 0
Active Links 0
Client API version 5.0.51a
MYSQL_MODULE_TYPE external
MYSQL_SOCKET /var/run/mysqld/mysqld.sock
MYSQL_INCLUDE -I/usr/include/mysql
MYSQL_LIBS -L/usr/lib -lmysqlclient_r
Directive Local Value Master Value
mysql.allow_persistent On On
mysql.connect_timeout 60 60
mysql.default_host no value no value
mysql.default_password no value no value
mysql.default_port no value no value
mysql.default_socket no value no value
mysql.default_user no value no value
mysql.max_links Unlimited Unlimited
mysql.max_persistent Unlimited Unlimited
mysql.trace_mode Off Off