I have three mail accounts on Thunderbird on my home PC - my home account, my office account, and my iCloud account. All were working fine until yesterday. This morning when I tried to download mail on my PC, I could do so for my home account and iCloud account, but not for my office account, although I could still download mail for all these accounts on my iPad. When I try to download load mail for my office account my my PC, the following message appears: "Unable to write the email to the mailbox. Make sure the file system allows you write privileges, and you have enough disk space to copy the mailbox." I am also unable to delete messages from my office account. Strangely, the name of this account in the left pane seems to have changed from "mail.hosei.ac.jp" to "Local Folders".