getting an error between versions

I am working in AutoCAD 15LT and my co-workers are using AutoCAd 2006LT.  When I create a file and one of my co-workers go in to update and save they are getting an error message and then getting booted out of CAD. (error handler reentered exiting now is what the error says).  I don't know how to fix the problem, my system back saves to version 2004 and updating everyone is not an option at the moment.  Any ideas on how to fix this problem???