Please post the exact commands you are using so as to receive better help.
This usually indicates a hardware conflict of some sort Run "ifconfig -a" and check the IRQ and I/O addresses used by the controller Your system might have a IRQ conflict.
To fix IRQ conflicts on PCI bus systems, you can often go into the motherboard BIOS setup and mark the conflicting IRQ as "Used by an ISA Device". This will force the motherboard to reassign the IRQ, often eliminating the conflict.
Double check the commands you are using for the card and make sure that it works normally first before using mac changer then try it with mac changer and then let us know what happens.



