AutoCAD has the ability to back save to any previous DWG version. By default AutoCAD will save to the latest DWG version it supports but you have the option to override this when saving. There are a few things to be aware of though, the newer DWG formats support the latest features in your version of AutoCAD.
Apr 18, 2013
I have just installed AutoCAD 2006 on a new PC, and for a while everything seemed fine. However when I save a drawing it comes up with the following: Unable to save to drawing (path and filename). Drawing saved to (path)savAE01.tmp It allows me to saveas without a problem. If I come out of AutoCAD and try to open the file I attempted to save, it is visible in the file list, but a message pops up saying: Cannot find the specified drawing file. Please verify that the file exists. I can rename the .tmp file to a .dwg file and it opens, but then if I try to qsave it, the same thing happens.