Backblaze will sometimes stop backing up certain mount points and external drives if the file name has changed. This is a Mac OS X issue that can often appear if the computer is restarted unexpectedly. The Apple support site reads:
If Mac OS X or Mac OS X Server is restarted unexpectedly, the current mount point listed in /Volumes may not be deleted and a new ("false") mount point with a " 1" appended to the name may appear (such as "My Volume 1"). This can cause issues for applications that rely on the path to certain files located in secondary volumes.
You can read the full article and find the fix here: http://support.apple.com/kb/TS2474?viewlocale=en_US