Unable to open the summary file for Sent on xxxx@gmail.com. Perhaps there was an error on disk, or the full path is too long.

Unable to open the summary file for Sent on xxxx@gmail.com. Perhaps there was an error on disk, or the full path is too long. I have tried to connect my second gmail account. The first one went ok. With the 2nd on the Inbox and All Mail folders initially gave this error, but Repair fixed both, Sent and all other folders have this error and Repair no longer fixes the problem. Then I noticed that I was then unable to delete emails from 2 inboxes including Thundermail inbox.