An error occurred during activation (can't sign into iMessage on Macbook)

I know many people have this problem, but none of the previous suggestions have worked for me. Basically, when I try to sign into iMessage or facetime, a message pops up that says "an error occurred during activation" or nothing happens at all after I click the "next" button. I've tried different solutions, but none have worked so far. If anyone else had this problem and managed to fix it, or if you know a way to fix it, please let me know!