If this was caused by "File Permission Settings" wouldn't it in the end prevent the files from being moved, written or changed?
The files are being written the where they are supposed to be. Why would a file permission issue cause an error but not prevent what the permission or lack thereof is supposed to prevent?
Not
necessarily. Windows has distinct permissions for Write Data and Append Data.
I agree that it is odd that it seems to apply only to DSF files, but this could be explained by filesystem location (if they're all in a subdirectory that has wonky permissions somewhere in the inheritance tree, by design or dumb luck, for example). There are also separate Syncronize permissions and other things that could conceivably cause errors in esoteric cases.
It is worth checking. If you can verify that the files in question are not read only, the files (and parent folders) are all owned by the proper user, and they all have "full control" permissions, then perhaps you've shown there is something wrong here. But until then, we can't be sure. I don't have any DSF files to test with, so I can't help with that.
If, instead, it is easier to post a few test files that cause it for you, I'll try them out later and see what I find.