I have a member who keeps getting a message saying 'Banned. You do not have permission to view this site' whenever they try to post on my community. They've been able to post before without issue. Their IP address isn't banned. Suggestions? Thanks!

Does the group(s) they belong to have access to the community? ACP -> Members -> Groups -> edit group -> Can access site?

Yes, their group can access the site.

Are they receiving this once they login or are they performing a certain action which triggers this error?

They're able to log in OK, but once they try to post in a forum they get the message (and they've also tried using a different browser and posting as a guest - same error message).

You may wish to try to disable Spam Analysis in ACP -> System -> Smart Community -> Features. To see if this is related to what is happening and Spam Analysis is blocking something here.

OK, I'll try that and ask them to see if they can post. Thanks!

They were able to post! Thanks so much for the help! The post was a job announcement - on its face it doesn't look any different from the dozens that are posted each week by other users, so who knows why it was triggering the spam filter. 

Our algorithm there is constantly getting tweaked so something could have stood out and triggered it. Glad things are working for you now though.