automated WordPress update has failed ???

I would appreciate a little hep with this, I’ve checked my site using Background Update Tester and receive the following message.

PASS: Your WordPress install can communicate with www.remarpro.com securely.
WARNING: A previous automatic background update could not occur. You would have received an email because of this. We’ll try again with the next release.
The error code was fs_unavailable.

PASS: No version control systems were detected.
PASS: Your installation of WordPress doesn’t require FTP credentials to perform updates.
PASS: All of your WordPress files are writable.

What does fs_unavailable mean? How do I fix it?

Many Thanks Ora