4.12.6 was released in July, 2006. Back then, buying Pro entitled you to 6 months worth of email support & free updates. Which means that you would have been able to download Pro until Feb/March 2007. After that, your email address wouldn't have been in LW's database any more & so it wouldn't be recognised.

Sorry, but your Pro's way out of date & you aren't elligible to download Pro for free.
LW don't keep those old installers for download anyhow - it's up to the user to save & back up whatever installers they download while their Pro benefits are current