corrupted MAC error -- fixed but not solved

[Gerhard Magnus]

Here's the problem -- fixed, but not solved:

A small LAN with three boxes and hardwired ethernet connections through
a router.
PuteF: server, running FC15 (x86) and LXDE  
PuteB: running FC13 (386) and gnome
PuteD: running FC15 (386) and KDE

I can transfer files between PuteB and PuteD using scp without any
problems. Regardless of which machine the scp is initiated on, all file
transfers between PuteF and PuteB, and between PuteF and PuteD fail with
the error message "Corrupted MAC on input. Disconnecting: Packet
corrupt. lost connection." The time this takes to happen varies within a
few minutes.

Things tried without success:
(1) installing a new ethernet card on PuteF and connecting it to the
router with a new cable
(2) connecting PuteF and PuteB using every possible combination of ports
on the router
(3) running a new long ethernet cable directly from PuteB to PuteF
(4) reinstalling FC15 (x86) on PuteF
(5) installing the 386 version of FC15 on PuteF

What worked:
Installing FC14 (x86) on PuteF -- which, obviously, is only a short-term
fix.

Is this a bug in FC15? Or a feature of FC15 that can't deal with my
older hardware? Assuming the latter, how old is "too old" hardware for
FC15? I bought the box (Intel dual core with 4GB memory) in 2007 from
one of those priceless dealers who builds them and is then a victim of
his success. There haven't been any problems with this box (despite a
lot of use) until a hard drive crash about a month ago, when I took it
into the shop for a full checkup. (Presumably this would have included
memory diagnostics.) The hard drives are also new. I started having
these problems as soon as I installed FC15 (x86).