Strange error message

[Roger]

I update my Fedora 19 every morning.
Booting up over the last 3 weeks pops up a peculiar error message: 
Software update failed to complete

The dialog says:
Failed To Update
the off line update failed in an unexpected way
Detailed errors from PackageManager follow:
The transaction did not complete.

  /var/log/messages shows nothing of note.
/var/log/boot.log has one error: [FAILED] Failed to start Wait for 
Plymouth Boot Screen to Quit.
See 'systemctl status plymouth-quit-wait.service' for details.
systemctl status plymouth-quit-wait.service
plymouth-quit-wait.service - Wait for Plymouth Boot Screen to Quit
    Loaded: loaded (/usr/lib/systemd/system/plymouth-quit-wait.service; 
disabled)
    Active: failed (Result: timeout) since Sun 2013-10-13 10:13:19 EST; 
43min ago
  Main PID: 544
    CGroup: name=systemd:/system/plymouth-quit-wait.service

I have run yum clean all.
How can I determine which update failed and what to do about it.

Thanks
Roger