Solaris NIS server and Linux NFS server

I have a Solaris 9 NIS server and Linux (kernel 2.6.9) NFS server. I
require access control on which machines can access what shares on the
linux NFS server. Hence i am using netgroups in /etc/exports. Also i
have set up hosts.allow and hosts.deny to have access control over
services like portmap, mountd, statd etc. From the NFS server i can
query netgroups NIS map properly. However when a legitimate request
come from a client computer to the Linux server, the server denies it.
If i use the IP address/Hostname of the client rather than netgroup in
the /etc/exports and /etc/hosts.allow, everythings seems to work well.

Has anybody faced this problem. Where am i going wrong? Any replies
would be highly appreciated.

TIA