Carefully check Your settings within /etc/exports:
The netmask is at least somewhat unusual. Did You really intend a 20bit mask instead of the (implicit) 24bit mask?
If You did not intend the 20bit mask, change the line to
or better to
Reexport (exportfs -av) and test again.
On the client, you can easily check a servers exports using
/sbin/showmount -e servername
If showmount fails, either the servers nfs service or the servers exports or the clients nfs utilities have not been set up correctly