portmapper

[Yoly Young]

System: Sun 4/280 running Sunos 4.0 . 

We keep getting the following kernel messages with increasing
regularity the past few weeks:

   vmunix: Portmapper not responding: giving up
   vmunix: Portmapper not responding: still trying

These messages occur when we shutdown; however the portmapper
doesn't encounter any problems getting started during bootup.
How do I go about finding out why it's failing?  
Reply by e-mail please.