Update sql query of multiple fields not working

Try

Code:

$this->db->where('WEBLOGIN', $WEBLOGIN);
$this->db->where('TIE_Codigo', $TIE_Codigo);
$this->db->update('TIENDA', $array);

or

Code:

$condicion = "WEBLOGIN = '{$WEBLOGIN}' AND TIE_Codigo = {$TIE_Codigo}";
$str = $this->db->update_string('TIENDA', $array, $condicion);

You don't need the transaction block if you are performing a single update.

I haven't tested the above code.

Good Luck.