What is the latest Aperture version? V.3.6 ?

I have a Macbook Pro and an iMac. Both have the latest OS installed. Aperture 3.6 works fine on the MB Pro. On the iMac when requested to load I get error message. :This version will not work with OS and directed me to the AP store to download a newer version. The AP store error message then states "The application you are requesting is not available for this use" ?????? Thanks,