File corruption when using kernels 2.6.18+

[Neil Romig <neil@romig.demon.co.uk>]

I am using kernel 2.6.17.14, and would like to use newer versions for the wireless code but I get file corruption with any kernel 
more recent than this. My system uses a SiS645DX chipset (it is a rebadged CLEVO D400E) with 5513 IDE.

I get this corruption with read/writes, i.e using "cp", "dd", when compiling software, writing to CD, etc etc. An example:

cp ../Changelog-2.6.18 .
diff Changelog-2.6.18 ../Changelog-2.6.18

16377c16377
<       LD      .top_vmlinux1
---
 >       LD      .tmp_vmlinux1
23954c23954
< Date:   Mon Jul 1% 04:45:11 2006 -0700
---
 > Date:   Mon Jul 10 04:45:11 2006 -0700
24955c24955
<     This is generally useful, but partacularly helps see if it is the same sector
---
 >     This is generally useful, but particularly helps see if it is the same sector
31879c31879
<     [MMC] sdhci: version bump cdhci
---
 >     [MMC] sdhci: version bump sdhci
42955c42955
<     Replace `he temp makefile hacks with proper CONFIG entries, which are also
---
 >     Replace the temp makefile hacks with proper CONFIG entries, which are also
49050c49050
<       and this task is(already holding:
---
 >       and this task is already holding:
[output clipped]

I would suspect a memory problem but memtest86+ gives no errors despite numerous passes, and I get no errors in older kernels. Does 
anyone have any idea what changed in 2.6.18 to cause such an error?

I have tried some obvious things (see thread on linuxquestions.org: 
http://www.linuxquestions.org/questions/showthread.php?t=578200), but I don't understand enough about the kernel to get any further.

Neil.