You might think this is a funny topic for an LT blog, since AutoCAD LT can�t create the special, intelligent objects used in vertical products like AutoCAD Architecture, known collectively as �AEC objects.� But it is relevant to a specific group � those of you using AutoCAD LT 2011 or 2010, and receiving files from people using AutoCAD Architecture 2009 or lower (or a similar vertical product). When you open a file from one of those products, you might see this message: Saving the drawing will update any AEC objects in it to the current version, which will be incompatible with earlier versions. Normally, round-tripping a drawing works just fine. In other words, if you create a drawing in 2007, work on it in 2011, then save it back to the 2007 file format, you can keep working on it just fine in 2007. (With the exception of proxy objects for newer object types � like multileaders � that weren�t available in the old version.) However, when you�re dealing with AEC objects, saving a drawing using a newer version � even if you�re saving it to an older file format � updates the special objects to the newer version. Now, when you send the drawing back to the person with AutoCAD Architecture 2007, they won�t be able to work with those custom objects any more. There�s nothing you can do about this � it�s just a function of the object types and the file format. If it�s only a one-way trip (if you never have to send the files back), then you have nothing to worry about. But if you see this message, and are planning to return the files at some point, you might want to make a copy before you do any saving.Go to the original post...