Your version of nvnet was compiled against a kernel with CONFIG_MODVERSIONS=y. Recompile nvnet against your current vendor kernel and try again.
Or, if you don't want to use the vendor kernel, you can download 2.4.23-rc5 from www.kernel.org,
which includes the new forcedeth driver. forcedeth is a clean-room reverse-implementation of the nvnet driver, and it has full source available.