Memory Errors are puzzling me

Hello Experts, this one has em puzzled.

I built a computer from spare parts I had accrued over a period of time.  It POST'd fine.  I checked CMOS Settings and left them at default as they look OK.  Tried to install from my bootable Windows XP Pro SP3 slipstreamed CD, but it failed with a BSOD:

"STOP: 0x000000024 (0x001902FE, 0xF79029B4, 0xF79026B0, 0xF70B9AF4)" ntfs.sys Address F70B9AF4 base at F7072000

There seem to be a few things that could cause this, so I concentrated on the "ntfs" aspect and suspected hard drive problems.  Ran Seagate Seatools (for Maxtor & Seagate Drives).  Quick and extended tests passed fine.  Just to be sure, I did a full wipe then ran the diagnostic tests again.  Everything was fine, but I got the same STOP error next time round.

OK, so it must be something else, so I individually tested my RAM (ie. one stick at a time) in 1st slot using Microsoft's "Windows Memory Diagnostics" and Memtest86.  Now, here's the odd thing.  Each individual RAM module passes the extended tests with no errors.  Add one of the other good modules in at slot 2 and I get errors.  Not immediately though.  With Memtest86, it is consistently in test No. 5 named "Block Move, 64 Moves".

Of course, it is possible that one or more of the tests after No. 5 would have shown errors, but I never got to that stage. What I have yet to do is run the tests one at a time in reverse order.  You will no doubt know and appreciate how long these tests take to run and therefore excuse the fact that I don't have full results to show.

My question really centres round why each separate memory module should pass the tests, but add one or two more modules and there are errors.  As far as I am aware the memory modules are pretty well matched.  They are certainly within spec for the motherboard, and the only difference is that two are Cas Latency 3 and one is 2.5.  Perhaps if I supply my system specifications one or more experts may be able to suggest the cause(s) of the problem.

http://global.shuttle.com/product_detail_spec.jsp?PI=624
http://eu.shuttle.com/archive/en/ak39n.htm#ak39n

As PDFs
Spec: http://image.shuttle.com/ResourceCenter/download_file.jsp?file_id=5838
Manual: http://eu.shuttle.com/download/Archive/Manuals/en/ak39_n/ak39en.zip

Shuttle AK39N Motherboard (VIA Apollo KT400-based) - ATX Form Factor, not an XPC board.

Compatible Processors: Socket A/462 Athlon, Duron, Athlon XP up to Athlon XP (Barton) 3000+ with 200/266/333 MHz FSB at time of writing.  I have an Athlon XP 2400+ currently fitted (333 FSB), and I'm pretty confident it is fine as I have tested it in another PC of similar spec.  It is cooled by a Thermaltake TR2 Socket A Ultra Silent Cooler which is running effectively.  No overheating problems to consider.

Memory Supported:  184-Pin unbuffered DDR SDRAM - 3 slots up to 3GB RAM supported as PC1600 (DDR200),  PC2100 (DDR266), PC2700 (DDR333), PC3200 (DDR400) modules with a clock frequency of 100, 133, or 166MHz.
I think I got the PC to DDR equivalents correct there.  PC3200 is DDR400, right?.
I have 3 x 512MB DDR400 modules to fit.  I am sure they are non-ECC unbuffered.  How do I tell without being in Windows to run Belarc, or whatever?  The RAM is being cooled effectively by case fans.  I measured temperature inside case and it's nice and cool.

Onboard VIA VT8235 is disabled at CMOS in favour of Creative Audigy 2 card.
Connect 3D Radeon 9250 SE 128MB 8x AGP (no integrated graphics to disable).
400 Watt Power Supply that has been tested in another computer of similar spec and works fine.
Maxtor DiamondMax9 40GB 7200 IDE HDD as system drive and Seagate 160GB 7200 IDE as slave.  Both drives pass fitness tests.
BenQ 16x DVD-Rom Drive and LiteOn Dual Layer DVD-RW SOHW-1633S DVD-RW.

You may have noticed (if you have read any of them yet) in the above linked pages the following statements in the specifications:

----------------------------------------------------------------------------------
FSB infinitely adjustable: 100 to 166MHz (in 1MHz-steps).
Note:
If an Athlon XP processor with 166/333MHz FSB is used, for KT400-chipset the DDR333-memory is essential, as only synchronous operation is possible on this setting.

3 x 184-pin for PC1600 (DDR200), PC2100 (DDR266) or PC2700 (DDR333) unbuffered DDR SDRAM memory with 100, 133MHz or 166MHz clock frequency up to 3GB capacity. Possibility for adjusting PC3200 (DDR400)
Note:
KT400-chipset requires at 166MHz FSB synchronous memory frequency at 166MHz (DDR333), as well.

Processor      FSB      Multiplier
AMD Athlon XP       2400+       133MHz 15x
CPU internal core bus speed runs at 200/266/333MHz.
------------------------------------------------------------------------------------

The above is relevant to BIOS Versions S024 and above.  The board came as BIOS version S024 and I haven't updated it yet.  I see no pressing need to, as it should support the CPU and memory as it is.

My Althlon XP 2400+ CPU has a 333MHz FSB.

OK, I see POST "Memory Clock is DDR400", so the BIOS knows it has PC3200/DDR400 fitted.

In the CMOS Setup Screen > Standard CMOS Features, it recognises and reports the true capacity of memory that is fitted.
Under "Advanced BIOS Features" the "CPU L2 Cache ECC Checking" setting is enabled, if that is relevant.

Under "Advanced Chipset Features", the DRAM Clock/Drive Control setting shows the following options:

DRAM Clock: By SPD, 133MHz, 166MHz, and 200MHz.
Currently showing FSB as 133MHz and DRAM Frquency as 200MHz when set to "By SPD", although I have tried the other DRAM Clock speeds also.  Setting to 133 shows "Memory Clock is DDR333" in POST, and setting it to "By SPD" shows "Memory Clock is DDR400" in POST, so I'm sure i have the correct setting.

DRAM Timing: Auto by SPD, Turbo, Ultra, and Manual. It's currently set to "Auto by SPD", although I have tried the other permutations with the exception of Manual.

The "manual" option allows you to set CAS Latency, Bank Interleave (currently disabled), Prechange to Active(Trp) (currently 3T), Active to Precharge(Tras) (currently 6T), and Active to CMD(Trcd) (currently 3T).  I have no intention of messing with any of these.

Other settings under the "Advanced Chipset Features >  DRAM Clock/Drive Control" page are:
DRAM Burst Length = 4
DRAM Queue Depth = 4 Level
DRAM Command Rate = 1T Command
Write Recovery Time = 3T
DRAM tWTR = 3T

Back under "Advanced Chipset Features", the "Memory Hole" is set to Disabled.  To be honest, I've never really understood that setting, so I don't mess with it.  I just included it in case it's relevant.

The last relevant page in the CMOS Setup Screen is "Frequency Control" containing the following current settings:
CPU Clock = 133 (that equates to a multiplier of 15x 133MHz = 1,995MHz, correct?).
Auto Detect DIMM/PCI Clk = Enabled
Spread Spectrum = Disabled.

Here are the apparently relevant values under the "PC Health Status" page of the CMOS Setup Screen (with the occasional very minor fluctuation not exceeding 0.01volts + and -):

CPU Voltage = 1.66v
DDR Voltage = 2.64v (is that correct?)
AGP Voltage = 1.52v
Chipset Voltage =  2.49v
3.3V VIN = 3.29v
5V VIN = 5.05v
+12V VIN = 12.60v
System Temperature = 29 deg C
CPU Temp = 39 deg C

So, going back to the FSB settings and the manufacturer's notes about DDR400 usage.

Do you think that any of those settings would have any effect on the errors being detected by Memtest86 and the Microsoft memory tester if I have them wrong?

Thanks in advance
Bill