[rdiff-backup-users] What does this error from rdiff mean?

[Chris G]

I am getting the following error every day from my rdiff-backup :-

    UpdateError sofdev/cprg/utils/fred File changed from regular file before 
signature

What does it actually mean and how do I get it to go away?  When I
first got the error I deleted the file sofdev/cprg/utils/fred and I
have just checked that it really isn't there any more but I'm still
getting the error message every time I do a backup.

-- 
Chris Green