Not sure if this is the case but check /var/log/messages and make sure you don't have a naming conflict. Check /etc/hosts, add the hostname to the ip. Could there be something on the hosts systems preventing access to data. Again try to create another share to test (data1).
I believe I know what the problem is. I played a little bit around with a new share as you suggested and connected it to different directories. Some dirs I could connect via nfs, some not. It might have something to do with the rights - we moved the server from a windows domain (NT) using ADS to a different domain using internal LDAP for authentication.
So all I need to do is to change the access rights what would be easy, if I would be able to mount the dirs via nfs...
If using Internal LDAP add users to the shares. This is explaned in the NAS Enterprise manual
pages 14 - 26. Once you have added your users then go to the Fuction of Users Shares Access and grant them access to the shares. Please review the manual. Manual can be obtained by clicking on the help tab then you see the manual button.