So I decided it had been too long since I have done a clean system install, and since I am having so many OS X problems, I decided to do a clean install. I found an old small hard drive, and wiped it and installed El Capitan on it.
After re-install I tried Messages, and low and behold, I still am getting the can’t authorize iMessage message! WTF! And I have a serial number in my about this mac, and have no replaced the motherboard or processors or even ram! THIS IS SO FRUSTRATING! It worked fine until El Capitan!
Honestly I can only think of one thing it could be, and I hope it isn’t. I have this Wifi and Bluetooth Card from MacVidCards to enable Handoff, Continuity and Airdrop. It worked fine in Yosemite, but maybe Apple did something to stop it in El Capitan, and that is stopping me from being able to use Messages in El Capitan. Maybe.
Going to also go through all my internet accounts and see if paring them down helps. I don’t know, this is so damn frustrating!