If you have Sony Vegas Pro 13, Sony recently shut down their servers that were used to register/activate Sony era programs. Fortunately, there is a workaround that enables Sony era programs to be registered/activated and the process is outlined in:
If you have unsuccessfully tried this or you have a version of Vegas Pro 13 that was released by MAGIX, you may need to lodge a support ticket with Vegas Support via the Support link in the forum's header.