@rich Urm: Have already replied per email, but will repeat here for the sake of people having the same issue:
Probably you have “license.key” file in the C:\Program Files (x86)\CintaNotes folder.
Please exit CintaNotes and delete this file.
Afterwards start CintaNotes and try to register the key again – should work this time.
@Irekfpl: Nikas is correct, please enter everything without brackets and quotes.