Re: I am trying to install a registered copy of Photoshop Lightroom that I never installed on my Apple iMac with software version 10.10. I get the message “Adobe Lightroom 1. Cannot be installed on this disk because a newer version of this software alre

Actually when LR 5 starts for the first time after it is installed it will have a dialog to Buy, Try or Enter a serial number. You select Enter a serial number and enter the LR 5 serial number first and then because it is an upgrade serial number it will ask for the serial number of a Previous version. You then enter the LR 1 serial number.