That's correct the keys, and therefore the install for the download
version are different from that for the boxed set.
Simply install your CD version over the top and enter the key during
the install. You won't lose any work you already did in the trial.
TWRcomputing are aware and advise it is necessary to reinstall the
from the CD - having done so, only the key code is requested when
validating the software and the process will go ahead just fine.