What is Illustrator CS doing to EPS files???

Hello all :-)

This is the darndest thing! I created a map in Illustrator CS (operating system is Windows XP), saved it as an EPS file, and when a service bureau tried to open it up in Illustrator (earlier version of Illustrator running on Windows 2000) it kept giving the operator an error message regarding the version. I thought an EPS file would not have any issue with versions since you certainly cannot choose any particular version when saving it like an AI file does. So, I told her to "place" the image into a page layout program and she ended up printing it successfully after the EPS was placed into PageMaker on a Mac!! This is the first time I've ever had any issues with an EPS file not being able to be opened in Illustrator. Does anyone have any clue whether this is an Adobe issue or maybe it has something to do with how Windows XP saves files??

Lauren