MademoiselleTink:
The Macintosh version is not 64 bit, only 32 bit, if you are on the Mac, download the Mac version. Otherwise, make sure you have downloaded the correct Windows version.
You should add a Signature to your Profile (click the Profile button near the top of this page) with your ArchiCAD version and operating system (see mine for an example) for more accurate help in this forum.
David