Renaud, We had tried with most of the troubleshooting steps. However , if you had not installed any other applications other than CC version apps, After performing below steps, when you launch any installed Adobe apps , it will ask to activate again. If you had installed any older version Apps like CS 4 , CS 3 , CS 5 , make sure that you have serial number with you. You may try with below steps : OR Close all Adobe applications and quit Creative Cloud desktop application. 1) Right click on Finder icon and select "Go-To" Folder option. 2) You will get a text box, type-in below command and then hit 'Return' key. /library 3)Then navigate to Application Support>Adobe. Open Adobe folder and locate folder named SLCache and trash all contents present in it. Also under same Adobe folder, locate folder named SLStore and rename it to SLStore-old. Then launch Creative Cloud desktop application and sign in with Adobe ID and Password, if already signed in , Sign out and sign in again. Then launch Lightroom application and try activating. If you still face same issuer , the only option left are removing all Adobe apps and remove Adobe folders from both ~/library and /library. There by performing complete removal and re installation process. Then install Creative Cloud and install Lightroom 5.7.1 and check. If you still face same issue , better to contact Adobe Customer Support via Live Chat. and confirm if the subscription is active . Also you can contact Adobe Technical Support via same Live Chat , they will check with the issue further , also they can even remote access your computer and check on the issue. I wish you all the best. You may contact Adobe Customer Support via Live Chat using below link : Contact Customer Care
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