[CentOS] Fedora and CentOS no longer on speaking terms

I have just upgraded my server from CentOS 5 to CentOS 6 and am having 
connectivity problems.  My laptop runs Fedora 14, and I have been in the habit 
of mounting data partitions on my server by fstab entries.  Since the update 
I've not been able to do that.  On watching the messages during a reboot I saw 
a statement that the connection was denied by the server (where are those 
messages stored so that I can quote accurately?).

I have temporarily disabled both the firewall and selinux, and the problem 
persists, so clearly they are not the cause.  Logwatch has the following 
section which may or may not be connected:

 --------------------- Connections (secure-log) Begin ------------------------ 

 
 Userhelper executed applications:
    anne -> system-config-users  as root:  1 Time(s)
 
 **Unmatched Entries**
    polkitd(authority=local): Operator of unix-
session:/org/freedesktop/ConsoleKit/Session2 successfully authenticated as 
unix-user:root to gain TEMPORARY authorization for action 
org.fedoraproject.config.firewall.auth for system-bus-name::1.88 
[/usr/bin/python /usr/bin/system-config-firewall] (owned by unix-user:anne): 1 
Time(s)
    polkitd(authority=local): Registered Authentication Agent for session 
/org/freedesktop/ConsoleKit/Session1 (system bus name :1.24 
[/usr/libexec/polkit-gnome-authentication-agent-1], object path 
/org/gnome/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8): 1 Time(s)
    polkitd(authority=local): Registered Authentication Agent for session 
/org/freedesktop/ConsoleKit/Session2 (system bus name :1.45 
[/usr/libexec/polkit-gnome-authentication-agent-1], object path 
/org/gnome/PolicyKit1/AuthenticationAgent, locale en_GB.utf8): 1 Time(s)
    polkitd(authority=local): Unregistered Authentication Agent for session 
/org/freedesktop/ConsoleKit/Session1 (system bus name :1.24, object path 
/org/gnome/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8) (disconnected 
from bus): 1 Time(s)
    polkitd(authority=local): Unregistered Authentication Agent for session 
/org/freedesktop/ConsoleKit/Session6 (system bus name :1.214, object path 
/org/gnome/PolicyKit1/AuthenticationAgent, locale en_GB.utf8) (disconnected 
from bus): 1 Time(s)
 
 ---------------------- Connections (secure-log) End ------------------------- 

An example fstab line is

/Data1			/nfs4exports/Data1	none	bind		0 0

Under CentOS 5 this was mounted by the exports line:

/nfs4exports/Data1  192.168.0.0/24(rw,insecure,no_subtree_check,nohide)

Following advice, I have changed this to:

/Data1/ 192.168.0.0/255.255.255.0 *(rw,sync,insecure,no_all_squash)

That hasn't helped at all.

I'm completely at a loss, and really need to get this connection working 
again.  I've done lots of googling and reading, but just feel to be digging an 
ever-deeper hole.  All help appreciated.

Anne