Problem getting past a login screen

Hitting a problem with getting past a login screen.

Whatever I do, I get a Status Code 403, and returned to the login screen.

It could be because the site is returning a cookie, and screen-scraper isn't handling it?

Or it could be because the button is not a button. It is a:
Accept
...Which is not actually a button, and is calling some JavaScript to do the POST thing.
And that madstudio.validar() contains some magic that screen-scraper cannot replicate?

...Though I have determined that the POST string is tl=foo&tp=bar&rl=0 and I reckon it
is getting sent correctly.

Any ideas?

Regards,
--
Mike