booting error on db1550 for kernel 2.4.31

[rolf liu <rolfliu@gmail.com>]

I compiled the kernel 2.4.31 using sde tools. Download linux to db1550
through yamon. but the kernel can't find the NFS root. I tried the NFS
system from other linux box, and the NFS is ok. Who met this same
problem?

Looking up port of RPC 100003/2 on 10.200.0.198
RPC: sendmsg returned error 128
portmap: RPC call returned error 128
Root-NFS: Unable to get nfsd port number from server, using default
Looking up port of RPC 100005/1 on 10.200.0.198
RPC: sendmsg returned error 128
portmap: RPC call returned error 128
Root-NFS: Unable to get mountd port number from server, using default
RPC: sendmsg returned error 128
mount: RPC call returned error 128
Root-NFS: Server returned error -128 while mounting /nfsroot/mipsel
VFS: Unable to mount root fs via NFS, trying floppy.
kmod: failed to exec /sbin/modprobe -s -k block-major-2, errno = 2
VFS: Cannot open root device "" or 02:00
Please append a correct "root=" boot option
Kernel panic: VFS: Unable to mount root fs on 02:00 

Thanks for the suggestion