Usually you get this error if the you are trying to using showmount command to see the available nfs shares on your remote nfs server.

If the nfs service is runnging on your remote nfs server, you get this error on your client machine after running showmount command.To resolve this issue, just check if the nfs service is running on your server or not

Simply restart the nfs service on server and also make it start at startup using chkconfig command