I had the same issue with my synology disk station. For me the following solution was helpful:
Perform System File Check (SFC), and then check if this fixes the issue.
Follow the steps:
a. Press “Windows Key + Q” to open Charms Bar.
b. Type “cmd” without quotes in the search box.
c. On the left pane, right click on the “cmd” option and select “Run as Administrator”.
d. Type “sfc /scannow” without quotes and hit enter.
Note: It may ask for windows installation DVD to fix and to enable SFC to make more than minor repairs. Some files saved on your computer might get deleted when fixing corrupted files.
(see also: http://answers.microsoft.com/en-us/windows/forum/windows_cp-performance/backup-error-0x807800c5/95959b0d-8f2b-4bcb-adb7-ecac48b6c239)
Thanks, but system file check made no difference.