I've used Win32::IEAutomation a few times...
I feel this error occurs when the page fails to load completely
and the other function tries to access it.
try this:

my $agent = Win32::IEAutomation->new(visible => 1);
$agent->gotoURL($URL);
$agent->getTextBox('id:',"tb")->SetValue($name);
$agent->getButton('id:',"cmd")->Click();
Wait_For_Complete_Load();

sub Wait_For_Complete_Load
{
    while($agent->{agent}->Document->readyState !~ /complete/i)
    { 
        sleep(1); 
    }
}
[download]

Check the wait_for_complete_load subroutine...
This is from one of my scripts and i've not changed
it to suit your purpose...but this will give u the
general idea