Currently Being ModeratedMar 24, 2012 11:42 PM (in response to emailobyrne)
Disconnect any external hard drive that's connected to a port on the USB card, before letting the computer go into sleep mode. If you're running OS 8.6, did you install the USB Adapter Card Support 1.4.1 after installing the card? Also, older Macs had problems with the brand of controller chip found on certain USB PCI cards. The consensus of opinion was that cards having an NEC controller chip caused fewer problems in Macs, than those with a VIA or OPTI controller chip. While this won't eliminate the sleep issue that you've described, the choice of card can affect overall compatibility. If you search the Power Mac Forum ("Expansion") for "sleep problems," you'll find many similar posts.
Currently Being ModeratedMar 25, 2012 11:36 AM (in response to Jeff)
Some USB PCI cards are not Mac-friendly. Please see this excellent discussion contributed by ASC's Superhero of the PPC Mac, "japamac."