I’ve had an AIM account since Messages was iChat. I’ve never used the AIM app, but I use Messages all the time. A couple of months ago, I could no longer log into my AIM account in Messages on my iMac. Today, I was no longer able to do so on my MacBook.
When I had the first problem in September, I found no way to get into the account, even though it worked on AOL’s website. I deleted the account in Messages, and tried to re-add it. Each time I did, I got this message:
But it turns out that what you need to do is not create an AOL account, but rather choose Other Messages Account, and select AIM from the popup menu:
Then it works. Go figure.
I still don’t know why the account I used for years stopped working…