If you cannot get it to repeat, it is likely a hardware problem. Possibly memory. If you do have bad hardware you will eventually corrupt your file system, so the problem should not be ignored.
See: http://www.bitwizard.nl/sig11/ I use and like http://reality.sgi.com/cbrady_denver/memtest86/ as a memory tester. VA also has a burn-in system you might dig up and try. good luck, BM
