Problem with SQL Server connection

I have a PHP system hosted on a Linux server that queries a SQL Server database through mssql . Works perfectly on the server. I needed to make some changes to this system, so I put it in my localhost and it was working ok. Out of all, queries with mssql stopped working, returning ERR_EMPTY_RESPONSE on pages.

The connection:

$host='******';
$user='***';
$database='****';
$pass='****';

$con=mssql_connect($host, $user, $pass) or die ("Erro de conexão com o banco de dados"); 
mssql_select_db("$database") or die ("Erro ao selecionar banco de dados");

The connection does not return any errors. But when I run a query like this:

 $sql=mssql_query("SELECT DES_MOVIMENTO, VAL_PRODUTO_MOVIMENTO
 FROM supervisor.MOVIMENTO_ESTOQUE 
 WHERE COD_PRODUTO='1254'") 
 or die ('Erro de conexão com o SIGA');

This error appears:

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