win2000 server NIC problem

My client has a dual processor,intel server motherboard,256 mb ram with
2 nics

1)Intel(r) 82559 fast ethernet adapter lan on motherboard and

2)Intel Pro/100 + pci adapter(which is installed on a pci slot)

The m/c has recently given the below errors.

System log
————

Intel(r) 82559 fast ethernet adapter lan on motherboard :Has determined
that the adapter is not functioning properly.

IT works perfect for say for 7 days and aburptly starts malfuctioning one
fine day,and after rebooting 3-4 times ,it works .

Whats the problem pl.I need it urgently.