There is a problem in the interaction between the Kernel nfsd and the rpc.mountd command. The kernel provides services for NFS version 2, but rpc.mountd registers itself as supporting version 1,2 and 3. This causes an NFS3 client (like SGI IRIX) to try to mount a linux filesystem using version 3, but whenever it tries to do any actual I/O on the filesystem, the I/O fails with a version error. I worked around the bug by fixing the NFS startup script to pass -V 2 -N 3 as arguments to rpc.mountd. A better fix would of course be to add support for NFS V3. It looks like there are bits and pieces of it in the kernel sources, but they did not seem to make it into the build.
*** This bug has been marked as a duplicate of 2973 ***