I have somehow gotten some XREFs associated with AutoCAD LT drawings that I can't detach. I use XREF to pull in a wire list from an Excel spreadsheet. Sometimes a drawing that doesn't need a wirelist will have that XREF listed and the status is often ! Not Found. Even if I find the XREF file, often I still can't detach it. I think I have promulgated XREfs over several drawing files where they are not needed.