imessage does not have appropriate credentials
Not sure what happen but in the past 3 days when I try to login to iMessage I get the message: Could not sign in to iMessage. The registering device does not have appropriate credentials. This is on my iMac Pro. I have an iPad, iPhone, and Mac Book which are all working with that iMessage account. I've seen a number of folks with responses to this problem some work and some don't. I've rebooted but I have not cleaned up my ~/Library primarily because I didn't understand the steps I needed to take. I tend to always take the latest OS updates when I'm able and I do it on all machines at once. So my Mac Book and Mac Pro were updated together.
Thanks for any additional insight someone can provide.
MacBook, Mac OS X (10.5.4), Mac Mini