[rdiff-backup-users] Why doesn't this error ever go away?

[Chris G]

I get this error every time I run rdiff-backup:-

    UpdateError Mail/In/inbox/new/1206493854.22988_0.th-shell-1 File changed 
from
    regular file before signature
    UpdateError Mail/In/inbox/new/1206498391.30151_0.th-shell-1 File changed 
from
    regular file before signature

I assumed it originally occurred because a file changed while rdiff-backup was
running but it would appear that once it has happened the error message never
goes away.

Is this a bug?  Is there something I can do to clear the error so I won't get 
a mail about it every time rdiff-backup runs?

-- 
Chris Green