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 
grub menu.

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.

                                Lee