can not get a host name

[Julie Xu]

Dear all,

One of remote machine I can not reach it. From my DNS server:
# host problem_machine.com.au
Host not found.
# nslookup problem_machine.com.au
Server:  localhost
Address:  127.0.0.1

*** localhost can't find problem_machine.com.au: Non-existent host/domain
But I can dig it!!!

If I use ip address for that machine, I can get host name and run
nslookup,dig.

Is my DNS problem or other side?? 
How can I find the problem??

Any comments will be appreciated

Thanks in advance

Julie