Error with Expect.pm on HP UX

I'm running into an issue when trying to create an Expect object on an HP UX machine.

The error is:
Cannot create a new IO::Tty from fd -1: Invalid argument

The process in question actually creates child processes that then turn around and create the Expect object. To me, the error would indicate that I might be running out of pty's, but the server is configured to have up to 512 open, so I don't think that is it (there are as many as 90 child processes created -- each with their own Expect object).

Any help as to what the error means or some idea as to where to look to possibly troubleshoot would be greatly appreciated.

O/S: HP-UX B.11.11
perl: 5.6.1

$self->{myFTPHandle}=new Expect;
    $self->{myFTPHandle}->debug($debug);
    $self->{myFTPHandle}->raw_pty(1);
    $self->{myFTPHandle}->log_stdout(0); # Suppress writing of sftp replies to stdout

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