The file is a hang-over from when his data tree was on a MacOS9 system. Under that OS and earlier the string delimiter was other than NULL, so it would be a legal filename back then. He just wants to delete the file. It is currently in his 'Trash' ( = 'Recycle bin') and emptying it fails. Unfortunately he has been able to create another file of the same name by using the Finder to copy and paste the name, but once set it cannot be replaced.
I don't know how the file was copied from the old OS9 system, but any raw inode level copy would work. It could even be the old OS9 Mac drive.