UPDATE : I have purged the package "nfs-kernel-server" and I have reinstalled it from scratch. it worked for some time and then...it gave the same error as before. so,this is a bug for sure.
UPDATE : I have purged the package "nfs-kernel-server" and I have reinstalled it from scratch. it worked for some time and then...it gave the same error as before. so,this is a bug for sure.