Summary:

Thanks to the advice from Aaron J. Grier and Karel van Houten I did a 

	>> test 3/memory 

and found out that there existed a problem on the two last memory banks.  I
reinstalled the memory boards and it is OK.  The machine now boots OK.

However, I (stil) cannot netboot it ;-(

--
Yiorgos Adamopoulos         -- #include <std/disclaimer.h>
adamo@dblab.ece.ntua.gr     -- Knowledge and Data Base Systems Laboratory, NTUA