time machine will not backup after initial backup
I have a Western Digital (WD) MyBook Essential external hard drive that I have backed up my imac using Time Machine. After 4 hours, it did a full backup to it. Now, it will not keep things up to date, and keeps erring out with "Unable to complete backup. An error occurred while creating the backup folder." Any ideas? Apple troubleshooting says to restart the computer, but that didn't seem to help.
iMac, OS X Mavericks (10.9.1)