Linux NFS4 client with AIX 5.3 NFS Server

I am using Redhat Linux client with kernel 2.6.18-128.1.10.el5 , nfs-
utils-lib-1.0.8-7.2.z2 nfs-utils-1.0.9-40.el5.

AIX Server is on v5.3 (5300-09-01-0847.)

I can mount an filesystem exported by NFS4 from the AIX Server onto
the Linux machine but all user and group names show as "nobody".

NFS local domain is set to the the same value on both sides.

I see error messages similar to the below in /var/log/messages

rpc.idmapd[12577]: nss_getpwnam: name '500' does not map into domain
'testdomain.local'
and
Module '/usr/lib/samba/idmap/rid.so' initialization failed:
NT_STATUS_OBJECT_NAME_COLLISION

I am doing RID name resolution againt an Windows 2003 R2 ADS on both
Linux and AIX .

Any ideas on what is wrong? I can provide more config files and logs
if necessary.

Thanks,

Yavuz