PatchCAD’s licensing system works by hashing together several key components of your computer (like the CPU’s serial number, motherboard’s serial number, etc.) into one long number that cannot be reversed into the source components that make it up. This long number is commonly called Machine ID. If one of the hardware components that are used to make up the Machine ID is changed, the Machine ID will no longer match the previous value so the software will think that this is a new installation of PatchCAD and will prompt for a new activation.
Simply log in to your account, navigate to Manage Activations and remove the existing activation for this computer. This way you will not lose any extra activations of the 3 allowed concurrent activations.
Note about Virtual Machine: When a virtual machine software like Parallels Desktop is updated, it emulates a new virtual serial number for some of the components used to generate a Machine ID. It is most likely you will be asked to activate PatchCAD when your virtual machine is updated. This is normal behaviour.