The option is greyed out and unclickable. I've very thoroughly checked whether there are any residual files from an old 2016 installation, but have removed all of them (directory, temp, appdata, programfiles, the works). However, it still comes up with this issue. I've tried installing 2015 and upgrading, but the Check For Updates .exe shows no updates available. Dno what else to try! Thanks in advance!