Thunderbird showing "Unable to locate mail spool file" on installing gmail account in ubuntu 13.04?

Make sure thunderbird is closed.

Just go to the file browser and type CTRL+H to reveal hidden files, then delete the .thunderbird folder.

After that, thunderbird should open fine.

I was creating a localhost only environment to test email sending during development and faced this error message.

The reason was: my user spool mail file was really empty.

To solve it, I just composed an email to myself and clicked on Get Messages. Spool created and problem solved!