P4SPA+ Dual Channel DDR 3200

I have just assembled a system based in the P4SPA+. I am using
Crucial 512MB PC3200 DDR memory modules, I flashed the BIOS to 1.0a.
In order to have the memory subsystem run in Dual Channel mode it says
to populate dimm slots 1,3 and / or 2,4. When I populated slots 1 and
3 (The Blue Slots) I ran into all sorts of problems. I could not
install windows as I received multiple file copy errors and finally
the memory error long beep at startup to indicate a bad module. While
I couldn't load the OS with both modules, it would work somewhat with
either module in slot 1. However I would still expierience booting
problems. When I placed the modules in slots 2 and 4 all of the
problems went away and the system has not had problems booting once.
Any insight into this would be appreciated.