we ran in trouble with xntpd. One 6.5 SP7 server will not sync anymore.

ntpq> peers                                                                   
 remote           refid      st t when poll reach   delay   offset    disp
==============================================================================    ntps1-0.cs.tu-b  2 u    4   16    7   496.43  -467443 6583.94

ntpq> as                                                   
ind assID status  conf reach auth condition  last_event cnt
  1  3516  9014   yes   yes  none    insane   reachable  1
ntp.conf is
server prefer
If I add the lokal clock as backup, the server will sync local in a short time.
Another 6.5 SP7 runs fine with same config.

Why is my condition insane? How can I get rid of this?