my %attr        = (     'RaiseError' => 1,
                        'PrintError' => 1,
                        'ChopBlanks' => 1,
                        'AutoCommit' => 0,
                  );
print "establishingh connection\n";
my $dbh = DBI->connect("dbi:Sybase:server=ETMA_NYDEV_DS;database=tss_d
+s_dev2","uid","******", \%attr);

print "preparing call to PerlTest sp\n";
my $sth = $dbh->prepare("exec PerlTest2 \@RetVal = ? OUTPUT, \@SomePar
+am = ? ");

$sth->bind_param(1, undef, SQL_INTEGER);
$sth->bind_param(2, "val1", SQL_VARCHAR);

print "executing...\n";
$sth->execute;

$sth->bind_param(1, undef);
$sth->bind_param(2, "val22");

$sth->execute;  # exec again...

print "rolling back...\n";
# lets rollback

$dbh->rollback;
$sth->finish;

print "finishing...\n";
$dbh->disconnect;

close dbh;
print "----disconnected------\n";
exit 0;
[download]

Works for me with DBD::Sybase 1.07_01, DBI 1.607 and Sybase ASE 15.0.3 Dev Edition, with the original order of finish() and rollback(), except that I had to add syb_chained_txn  => 0, into the %attr because otherwise I got "Stored procedure PerlTest2 may be run only in unchained transaction mode."

Maybe there's something spicy going on with your mix of CHAINED/UNCHAINED mode, AutoCommit status and whatever's inside the stored procedure. I used just

create procedure dbo.PerlTest2(
 @id integer = NULL OUTPUT,
 @SomeParam varchar(100)
)
as
begin
 INSERT INTO test (stuff)
 VALUES (@SomeParam)
 SELECT @id = @@IDENTITY
end
go 

Grant Execute on dbo.PerlTest2 to test 
go

sp_procxmode 'PerlTest2', unchained
go
[download]

Update 2009-09-17: tested with newly built DBD::Sybase 1.09. Works correctly as well.

Update 2009-09-17 number 2: you can get the 1.09 for ActivePerl 5.8 by ppm install http://jenda.krynicky.cz/perl/DBD-Sybase.ppd

Jenda
Enoch was right!
Enjoy the last years of Rome.

THANKS --- Now I see what I was doing wrong --- i was setting the syb_chained_txn => 0 on a sth instead of dbh .. Thanks again!