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?

I had /have a Robocopy Script that was setup to copy files from a Workgroup computer to a Domain shared network Folder that was working for about 2 weeks but isn't now. Is there a Robocopy Script ...