Since I wasn’t able to login to the online service, I finally found solution that maybe work for you.
Problem: Receiving error code A.B.C.D.E.F.-.H.I.J.K.-.-.N.-.-.-.-.-.-.U. when trying to login to online service.
Solution: Force changing your IP address.
You can do this by simply resetting your router or cable modem, since you have an internet provider with a small or immediate lease time.
In my case this didn’t work because my provider has a lease time about 24h. Means that I have to disconnected my cable modem longer than 24h to receive a new IP address. In my opinion that isn’t worth 😦
So, finally if you are owning a mobile phone which provides tethering you can share your mobile internet connection with your (in my case) PS4. Simply check your phone settings for a tethering / hotspot / access point option. Configure and enable it. Go to your console wireless network settings and connect with your phone.
That did the trick for me.
So I hope this will get you ready to play BO3Beta for at least a few hours.
Update: PS4 beta period is over. Unfortunately Activision or Treyarch (whoever is responsible for this issue) could not fix the problem. I just played one match, using my mobile phone as hotspot for the PS4 as described above. Hopefully PC and XONE players will be spared from this annoying error.