Yes, the IP Gateway seems to be incompatible with some Ethernet cards. Whenever the IP Gateway software is invoked, some Ethernet cards may cause the computer on which it is installed to lock up. You must press the restart button to get the machine running again.
The Apple IP Gateway was tested with some third-party Ethernet cards (no list is available) but obviously not with all. If you are having difficulty with your particular Ethernet card, contact the vendor for your specific card.
The Tech Info Library articled titled "Locating Vendor Information" can help you search for a particular vendor's address and phone number.
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