This 50MHz upgrade, an accelerator card or a clock boost on the motherboard? If its an accelerator, remove it and see if it works. If its a motherboard clock hack, then you need to revert the IIci back to it 25MHz as the I/O can't go that fast. TCP/IP should have picked up the card without the driver with only basic service; the driver adds to basic services of TCP/IP.

As is, a 25MHz Mac IIci is more than enough for basic network file services as everything is based on the speed of the I/O and the network and not the CPU.