Dual Connection and Database Connectivity Failure

[eluser]pakistanvoices[/eluser]
HI, I have write a code with dual connection in codeigniter. I am facing problem that it loses the database connection

Message "Unable to connect database using provided setting"

I am wondering, why is it going on ? Is there any bug or I am doing any mistake.

Database file setting is given below.

$active_group = "db_write";
$active_group = "db_read";
$active_record = TRUE;


$db['db_write']['hostname'] = "root";
$db['db_write']['username'] = "sb110";
$db['db_write']['password'] = "sb110";

$db['db_read']['hostname'] = "root";
$db['db_read']['username'] = "sb110";
$db['db_read']['password'] = "sb110";

$db['db_write']['database'] = "sb_dev";
$db['db_read']['database'] = "sb_dev";

$db['db_write']['dbdriver'] = "mysql";
$db['db_read']['dbdriver'] = "mysql";

$db['db_write']['dbprefix'] = "";
$db['db_read']['dbprefix'] = "";

$db['db_write']['pconnect'] = TRUE;
$db['db_read']['pconnect'] = TRUE;

$db['db_write']['db_debug'] = TRUE;
$db['db_read']['db_debug'] = TRUE;

$db['db_write']['cache_on'] = FALSE;
$db['db_read']['cache_on'] = FALSE;

$db['db_write']['cachedir'] = "";
$db['db_read']['cachedir'] = "";

$db['db_write']['char_set'] = "utf8";
$db['db_read']['char_set'] = "utf8";

$db['db_write']['dbcollat'] = "utf8_general_ci";
$db['db_read']['dbcollat'] = "utf8_general_ci";


$db['db_write']['dbprefix'] = "";
$db['db_read']['dbprefix'] = "";

$db['db_write']['pconnect'] = FALSE;
$db['db_read']['pconnect'] = FALSE;

$db['db_write']['db_debug'] = TRUE;
$db['db_read']['db_debug'] = TRUE;

$db['db_write']['cache_on'] = FALSE;
$db['db_read']['cache_on'] = FALSE;

$db['db_write']['cachedir'] = "";
$db['db_read']['cachedir'] = "";