I periodically do a mass copy/paste of all the file folders from my W7 "HomeServer" to a separate machine which is now running W8.1. I also use Acronis to back up this information daily to a separate disk on the server. For some unexplained reason many of the folders and files I copied and pasted from one of the disk drives on the server to the W8.1 system "disappeared" on the server disk. Everything got pasted to the backup drive on the W8.1 system OK. I check the Smart information on the source disk using the WD Diagnostic program and it said the drive passed with no issues. I copy/pasted the stuff back to the W7 HomeServer disk from the W8.1 system and all is well! I've never had anything like this happen in the past running W7 on all the systems on the home network. Any ideas on what could have caused this to happen would be appreciated.