>Which distribution are you using?  The latest is:
>	ftp.netbsd.org:/pub/NetBSD/arch/sun3/install-11-p1

First, I used the /pub/NetBSD/NetBSD-1.1/install, but now I tried
install-11-p1 with almost the same result:

----------------------------------------------------------------------
[...]
Sun Workstation Model Sun-3/50M.
ROM Rev 2.8, 4MB Memory installed, Serial #17509.
Ethernet address 8:0:20:1:F4:E.
[...]
>b st()
Boot: st(0,0,0)
>> NetBSD tapeboot [$Revision: 1.3 $]
466492+284060+87436+[41700+45456]=0xe1ddc
Starting program at 0x4000
Invalid Page Bus Error:
  Vaddr: FFD87200, Paddr: 00001200, Type: 0, Read, FC 5, Size 2>
----------------------------------------------------------------------

"Invalid Page Bus Error" appears immediately after "Starting program".