MIT-MAGIC-COOKIE-1 ID: -1 problem

[aroushdi]

I have a queer problem , and i would like have an explanation :
on certain linux machies , i can telent , ftp however  i get the 
following when logging to linux05 xxx.1.100.139 all addresseses resolve 
properly :

the commmand line to fire
xwin :20 -query linux05 -from xxx.1.100.216


AUDIT: Mon Feb 28 13:41:39 2005: 2172 xwin: client 1 rejected from IP 
xxx.1.100.139
   Auth name: MIT-MAGIC-COOKIE-1 ID: -1
AUDIT: Mon Feb 28 13:41:51 2005: 2172 xwin: client 1 rejected from IP 
xxx.1.100.139

I am using XDMCP and the amazing thing is that from other machines other 
than 139 i can get the xdm

Thks for ur help