Hi Kessi,
I checked your serial number with the 3.3.5 installer and it worked on my system. The serial number is all letters, so be sure to use lower case l, and not the numeral 1 - this has happened to people in the past.
The other problem that people run into is downloading the full version instead of the elements version. The one you want is Curvemeister for Elements v3.3.5.
If that's not the problem, let me know and I'll help get the new version up and running for you.
Mike