Lynne Allen has found a nifty little feature lurking within the COPY command, it allows a quick array to be created!
One of my colleagues had this issue today and we could not work out why the file would not detach. Apparently this is due to the XREF being in Paperspace and currently a forced detach of an XREF in paperspace is not possible. The XREF needs to found (QSELECT is your friend) and deleted prior to the detaching.
I expect you already know about http://lynn.blogs.com/ which is a great haven of AutoCAD knowledge. I don’t expect to rival such a blog but I hope to offer my own ideas, comments and tips that should be helpful for all AutoCAD users!