Within the last couple of days, while using Thunderbird, my list of unread emails disappears and I get a box that pops up that says: "The folder 'inbox on johnking2@comcast.net' could not be compacted because writing to folder failed. Verify that you have enough disc space, and that you have write privileges to the file system, then try again." If I click OK, my list of emails returns for a short while. I have no idea what to do, as nothing has changed, that I am aware of. I have a SD hard drive with about 17% space available. This is on a Dell laptop with i7 processor. Please help!