If your CB 6 license is already on the USB dongle then you should be all set and no reactivation would be necessary. Just install your software (CB 6) to use it. When you want to upgrade just purchase the correct software, install it, and it should work (make sure the dongle is connected).
If your eLicenser dongle is giving you issues, install the latest eLicenser software and run the maintenance. Run the eLicenser as administrator if it still is giving you issue. After that… if still having issues, then a support request to Steinberg is necessary. To fix your MySteinberg account, as Steve said, contact Steinberg support.