I'm using RoboCopy to backup computers on my network. I've written a simple *.cmd file with the RoboCopy commands in it so that users just double-click the icon to back up. For my remote users ...

You could also add a "/V /FP" to your robocopy command to see if it's even touching it and hopefully, if it is, see why it's not deleting it. It's not part of a DFS/FRS volume, is it?