"He who marches out of step hears another drum." ~ Ken Kesey
It tells you in the notification message. The file is compressed. Tell your client to TURN OFF compression when saving from illy. Newer version of Illustrator use this compression. The file should open just fine in X5. Shoot me a email and I will send you the file in a DRAW X4 format. Yet for future reference is they turn off compression when saving the files you shouldn't have any issues opening in DRAW. richard at fluiddsn.comscratch that. There are two (2) fonts that need to be converted to curves / outlines before resaving.
Asking your clients to save something a certain way will piss enough of them off that you will be better off in the long run by getting the right software.....Do not make your problem, your client's problem....