Please rename the library file from "Door 24 .dxf" to "Door_24.dxf" (note that two spaces have to be removed or replaced, one before the number 24 and one after it.
Basically, block names may not contain spaces. When creating blocks, QCAD prevents you from using spaces but when inserting a library item, the file name of the item is used as block name which produces this problem. Thanks for bringing this to my attention. This problem will be fixed in the next release. Most likely QCAD will simply replace spaces and the likes with underscores to create valid block names from file names.
Bug tracker:http://www.ribbonsoft.com/bugtracker/in ... ask_id=725