Running IMAP - was running version 52 and now version 60.0 beta - same problem. I have four AOL email accounts all set the same way, and only one is having an issue synching with the AOL server. The error message Thunderbird generates reads the same for each sub folder it attempts to open on the server. Thinking that one of my folders on my desktop was corrupted, I deleted the account and folders and re-created it. Same problem as previously described. It almost seems like the client is requesting an open/create with a syntax error or there is an indexing error, or a folder on the server that had been clobbered somehow. AOL is no help, won't refer to second line support.