I'm trying to reinstall LR5 on my Mac (yosemite) but I'm having problems. When I manually uninstalled the previous version following the instructions on the adobe website, I could not find the Lightroom 5 Registration file and now it won't let me enter my serial no. It just jumps straight to the request code page of the activation process. I've deleted the LR preferences folders but still no luck. Help! I don't have the previous serial number as the software was already on the PC when I bought it second-hand.