RIS - NIC driver issue

Folks:

I have been able to successfully install remote pc's using RIS, both of
these PC's have had Intel NIC's installed. I have a Dell Optiplex GX150
that uses a 3com NIC which says "3Com 3C920 Integrated Fast Ethernet
Controller (3C905C-TX Compatible)".

I've downloaded the drivers for this NIC and placed them in the I386
folder of the RIS server, just like I did with the Intel NIC drivers.
When I boot a GX150 into the RIS windows setup it tries to load the
network interface and gives the following error message: The file
el90xbc5.sys is corrupted. Press any key to continue".

I've tried different versions of this driver and to no avail. I don't
believe this driver is corrupt at all and the NIC works fine otherwise.
Anybody have any ideas what I'm doing wrong?