For some reason the nfs service has disappeared from your /etc/services file, NIS map or NIS+ table. You need to have an entry like:
nfsd 2049/udp nfs # NFS server daemon (clts) nfsd 2049/tcp nfs # NFS server daemon (cots)
If you use NIS+, you must make sure that the NIS+ entry is readable for the machine executing nfsd.
If you used your SunOS 4.x services file, that would explain it: SunOS 4.x doesn't have an entry for nfsd in /etc/services, Solaris 2.x requires one.
This will usually not happen until you upgrade to Solaris 2.4 or a later revision. Solaris 2.3 and earlier would always consult /etc/services, regardless of what nsswitch.conf said. /etc/services does contain the right NFS entries.
Solaris 2.4 and earlier don't have an entry for NFS over tcp, so this error is also likely to occur on 2.5+ NFS servers that are NIS/NIS+ clients of 2.4- servers. In 2.5 the error message will look like:
nfsd: Cannot get address for transport udp host \1 service nfs nfsd: Cannot establish NFS service over /dev/udp: transport setup problem. nfsd: Cannot get address for transport tcp host \1 service nfs nfsd: Cannot establish NFS service over /dev/tcp: transport setup problem.