Can't access files on WD hard drive created by Sync program

We have a customer who bought a Western Digital external USB hard drive.  They "backed up" their files regularly using the built in "Sync" software than came installed on the WD Passport drive. A few days ago the hard drive in the computer crashed and now the user wants to get his data off the external drive that he has been backing up all this time.

All they really care about is the "My Documents" directory.  They set it up to sync the "My Documents" a long time ago and it must have asked for (and stored) a password, because it is now requiring a password to restore the files.  He gave us all passwords he has ever used, but none of them are working.  From our research the files appear to be encrypted with dmailer or DmailerSync software. We called Western Digital and their only answer is "you shouldn't use the sync software as a backup, so we can't help you".

Is there a way to decrypt these files?  Or reset the password?  Or recover the password?