I'm not fully sure about your current configuration(maybe you can post some output from your config files).Maybe you can post some details about the users on both machines, the rights they have, groups created,
But mainly there are 2 issues that occur all the time when it comes to NFS rights:
http://nfs.sourceforge.net/nfs-howto/ar01s07.html#pemission_issues
Also, this might be a "stupid" answer, but make sure you restarted the systems (or the services) correctly in order to sync them.
Maybe also change nfs=4 to nfs4 (not sure if this affects anything, but I've never seen nfs=4 in fstab configs).