Have you tried what gmax had suggested?
Enable tracing right before the prepare_cached() and see what you get;e.g.,

DBI->trace(2, 'dbitrace.txt');
$sthn = $dbh->prepare_cached("SELECT DISTINCT nome FROM usuarios WHERE
+ login=? AND filial=?") or die "ERRO!"; 
$sthn->execute($gerente, $filial);
[download]

Run your program and see what you get in 'dbitrace.txt'

--perlplexer