I just got off of a chat with Adobe support trying to install PE 15 and Premiere on my Mac Pro as a second computer. When I try to put the serial number in it says "this serial number is not valid for Adobe Photoshop Elements 15" The original purchase was on windows and installed with that serial number with no problem. My understanding when purchasing them was that it could be used on two computers Mac or Windows? Then they first said I would have to deactivate my windows program and they would give me another serial number that would work for both. then they came back and said I would have to purchase another license for the Mac???