HP-UX 11.23 ping failures to windows systems

[S.K.]

Started as complaint that several WIN Server 2003 ENT SP2 (32 and 64-bit) systems could not telnet to HP-UX Itanium system on same data center subnet e.g. (not actual):
hpux 102.202.77.24 WIN could sometimes not telnet to or ping (start/run/ping) hpux 102.202.77.235. These are on same vlan so no routing.
I found same problem on the hpux trying to ping the same WIN systems. Sometimes WIN would respond to first packet, then no more and ping would just hang on hpux. Sometimes WIN systems will not respond to any pings, or all pings for a few minutes, then stop. Re-attempting pings to same hosts would change. Appears like a hardware nic problem.
However, there are 70-80 other Solaris, AIX, HP-UX, and Linux hosts on that same subnet 77 that were pinged from hpux successfully first time/every time. It is only the WIN systems on the same subnet 77 that don't respond, but inconsistent.
Other WIN systems on different subnet 76 do respond to ping. Have tried nsswitch.com with 'hosts: files nis dns' and 'hosts: files dns nis' and makes no matter. resolv.conf has correct domain and nameservers setup.
Our network team sees no switch, etc., problems. They did a 10k ping from switch and I had to disable 'source quench'.
Is this a hardware problem or do I need some special rx2660 gigabit patch?
Any ideas?
Thanks!# ifconfig lan0
lan0: flags=1843
inet 102.202.77.235 netmask ffffff00 broadcast 102.202.77.255
# netstat -r
Routing tables
Destination Gateway Flags Refs Interface Pmtu
localhost localhost UH 0 lo0 4136
hpux hpux UH 0 lan0 4136
102.202.77.0 hpux U 2 lan0 1500
loopback localhost U 0 lo0 0
default 102.202.77.1 UG 0 lan0 0