Memory works fine separately, but not together

I've been given four 1GB Corsair DDR2 memory modules, and am trying to fit them into my computer but am getting BSOD on Windows XP and errors in Memtest86+.

I've tried to identify if one particular module is faulty by trying them in pairs. They work fine in pairs, but when all four are inserted, Memtest86+ reports errors.

The motherboard is an Asus P5N-E with dual channel support and the modules are all the same model (same speed, capacity and timings) but one pair is a different hardware revision. One is v2.1 and the other is v2.2... the voltages are the same too. Would this minor difference be a possible cause of the problem?

I've got the BIOS memory timing settings all at AUTO - should I manually set the timings?

If you have tried both pairs, and had not errors, clearly it is due to some slight difference in the hardware. I would use "System Information for Windows" and check out your memory timings, and then compare them with a search on the Internet for the specs for your RAM, both revisions.

Then set your BIOS to match the timings to the slower spec.

http://www.gtopala.com/siw-download.html (free version at bottom)