Several years ago I finally had enough in regards to AutoCAD and the dreaded Z coordinates of objects always getting screwed up, usually after I xref'd in a consultants .dwg. Now, the issue wasn't that consultant's file, it was how AutoCAD works and me. If I snap to something 400 feet below, well it's my fault for not being aware. It was a tough thing to accept at first but once I realized that the error was in a belief of mine I was able to begin the path to enlightenment...at least in the realm of CADworld.
After all it was only a belief of mine that the lines "were" or worse yet "should" be flat. (Those @*^#! 'unrealistic expectations' will get us every time!!!) ...I mean they "looked" flat and I was in my top view...
"uh oh, 'better check the side view...@*^#!" Sure enough, the lines were not coplanar. AutoCAD may be a lot of things but it usually doesn't lie!
One thing that I got from all of this (and I can't be happier about it) is the realization of this whole system of CADbelief that exists mostly just below our conciousness. It is so nice to be free, or at least getting there, as the struggle for my freedom from CADbelief goes on; just now with my eyes open (er).
Well to make a long story longer, I suggest that in addition to using the solution on this Blog that you read the white paper from Autodesk (Make non-coplanar objects coplanar) for this one, as they explain 2 ways of achieving the desired result. They also provide a great deal of support there, as they always do. (I believe (hahahaha) that their syntax is incorrect, as I used the ^C^C in the command, they only have one ^. I can attest that the button works as you can see the command in the CUI dialogue image above, if you click on it.
'That said here's my favorite way, their example #2...Make a custom button and paste in the following syntax to the macro area within that button in the CUI:
Then just click that new button whenever you have objects at incorrect Z coordinates; no need to select anything first, this works on everything (no it won't explode walls in ADT, etc) but it will bring xref's down to a Z of 0 so unload if need be.
The screen shot at the top of this post is the CUI editor and If you don't know your CUI then introduce yourself by typing CUI at the ACAD/ADT, etc. 2006 and 2007 Command Prompt!!!
If you've never been there then please click the link on the CUI dialogue box that says "Learn more about Customization" the CUI is a subject for another time (in this Blog).