Why can't I connect dyndns using php?

[VIGIN]

Dear All,

I am trying to connect my Sever using dyndns with php code.
My Code is

$dsn = 'DRIVER={SQL Server};SERVER=xxxx-xxxxx.dyndns.org,1028\SQLEXPRESS;DATABASE=Cxxxxxxx6'; 
$connection = odbc_connect($dsn,'sa','xxxxxxxx') or die('ODBC Error:: '.odbc_error().' :: '.odbc_errormsg().' :: '.$dsn);
 

but showing error like:
Warning: odbc_connect() [function.odbc-connect]: SQL error: [Microsoft][ODBC SQL Server Driver][DBNETLIB]SQL Server does not exist or access denied., SQL state 08001 in SQLConnect in C:\wamp\www\qamaruae\components\com_amc1234\views\ amc1234\tmpl\statement.php on line 3
ODBC Error:: 08001 :: [Microsoft][ODBC SQL Server Driver][DBNETLIB]SQL Server does not exist or access denied. :: DRIVER={SQL Server};SERVER=xxxx-xxxx.dyndns.org,1028\SQLEXPRESS;DATABASE=xxxxxxxx

Please tell what happened?

Thanks
Kurakar