One of the problems with saving down is that not all of the fancy features in the new version readily convert to the old version. I've had a similar problem saving down from vanilla Autocad 2010 to 2004 for one of my customers. Mleaders do not translate, for instance. What you will probably have to do unless you can convince them to upgrade is to use the older entities. Going back the mleaders for instance...I have to use the old "leader" command instead of mleader when I wish to save down. You'll probably have to experiment with ways of generating geometry to find something that works with your other office.