I have seen a few of these lately, and wanted a new clean thread that will
come up in a search. I especially wanted the links in it. The m0n0wall
filesystem is held in ram. The only time the "hard drive" (be it a true HD,
a CF, or a CD and floppy) is accessed is on boot, saving config, or updating
the bios. Any other time you are only in ram. So a corrupt filesystem
often means corrupt ram.
The simplest way to test a PC like platform is a boot CD. My preference is
the Ultimate Boot CD. http://ubcd.sourceforge.net/ Some like the Ultimate
Boot CD 4 Windows, but I find it takes longer to boot, and it has less
hardware testing tools.
Other bootable CDs include any Ubuntu Live CD, and choosing memtest86 at the
Overclockix http://overclockix.octeams.com/ is a knopix CD with a lot of
hardware pounding stuff including memory and CPU testing.
If you test your memory extensively with 2 different methods, and it comes
back good, test the CPU. A faulty CPU can cause problems. CPUburn is a
good choice here. It is on UBCD and overclockix.
If the memory and CPU are both good, you can also try changing the NICs.
Some are better than others, and many just have a conflict with a given
configuration. If you still have no luck after this, you have a real
problem, and post it up to the list.