Strange error "\ip" do not work "\hostname" works

Very strange error, I will appreciate your help

When I'm trying to connect to a remote share from a Xp client to a W2000
server by IP, It doesn't work, It continously prompt user validation.
When I try by hostname It's work, very strange!

Both Machines are in the same domain, across a Wan link , Xp client at one
side with the DC and the Windows Server at the other side.
There isn´t a firewall filtering the link

At the server an event 5719 "No windows NT or DomainController available...
The remote procedure call failed and did not execute" appeared every 2 hours.

It seems a "ntlm" problem, I activated the netlogon.log
why the NlSessionSetup: Session setup Failed?
It has some relationship with my problem, thank's in advance


this is the output

08/06 12:23:52 [CRITICAL] AMERDM: NlSessionSetup: Session setup: cannot
I_NetServerReqChallenge 0xc002001c
08/06 12:23:52 [MISC] Eventlog: 5719 (1) "Domain-Name" 0xc002001c c002001c
.....
08/06 12:23:52 [SESSION] AMERDM: NlSetStatusClientSession: Set connection
status to c000005e
08/06 12:23:52 [SESSION] AMERDM: NlSetStatusClientSession: Unbind from
server \\domain-controller.aaa.bb.cc.com (TCP) 0.
08/06 12:23:52 [SESSION] AMERDM: NlSessionSetup: Session setup Failed