SmartWare not backing up modified file

I recently bought a 2TB My Passport drive.  The initial backup ran fine.  However, I have one 13GB file that was changed and it is not backing up the new version.  Instead, the backup ends with “Partial backup accomplished…” and the file is in a perpetual “File pending backup” state.  Smaller Word documents are backing up when they are changed so it seems to be just this one file.

My computer is running Microsoft Vista Home Premium 32-bit.   Have downloaded and installed all the recent firmware, driver and software upgrades.

Also checked that no other processes are using the file  (have run the handle and psfile sysinternals to verify).

I get the same results even if I switch to File Backup mode and select just that one file (Partial backup accomplished;  File pending backup)

I opened up a case with WD support more than a week ago and not getting any response.   Would anyone have an answer?

What type of file are you trying to backup? 

It’s an encrypted file with a unique extension.  It was backed up in the initial backup run.

*** UPDATE ***

Problem resolved.  Heard from WD Support.  They had me change the Volume Shadow Copy service from disabled to Automatic.   After a short while the file was backed up.    The other alternative was to copy and paste the file to the WD drive (but not in the SmartWare folder since they speculated that may cause a problem with the SmartWare backup going forward).