If the port the NFS client is attempting to use is greater than 1024 this error will occour. Use the insecure option in the /etc/exports file. e.g. /nfsMountDir/ *(insecure,rw,async,no_root_squash)

Don’t use this configuration for production environments. Source http://www.itsprite.com/linux-the-way-to-resove-mount-nfs-access-denied-by-server-while-mounting/