The activation relies on several pieces of hardware and software, including the OS, to uniquely identify the computer being activated. In the case of an OS upgrade to Windows 10, the OS ID changes, so the activation is no longer valid. Transferring the activation is only partially possible in the Administration client, but doesn't stick, since the computer ID sending the request isn't the same as the activation ID.
Call or email Hawk Ridge Systems Support in order to have the activations for your serial number cleared. This will allow you to reactivate them.