I don't know if everyone knows this but the best way to remove Excel spread sheets that have been attached to drawings is go into the data link manager Simply type the datalink command and the dialog box will appear. In here, all the spread sheets that have been attached to the drawing will be listed. Just right click on one of the files and select delete. The reason I brought this up was because I helped a fellow coworker today with this same issue that he could not figure out. He wanted to remove these files that were listed in the xref manager but it would not let him. I simply walked over and provided him the command to do this. Anyways I hope this helps a few of yall techs and designers.