Lost Database Connection

When I use this code:

PHP Code:

$this->db = \Config\Database::connect($this->base_datos);
$this->query = $this->db->table($this->db_tabla);
$this->db_columnas = $this->db->getFieldNames($this->db_tabla); 


I get the error:

ErrorException: pg_escape_literal() expects parameter 1 to be resource, boolean given

If don't call getFieldNames the error desapears.

Thanks