Why can't install more than 3 RAM modules on Intel S2400SC?

Question

Iron

Good afternoon.
There is an Intel S2400SC board and one Xeon E5 2407v2 processor.
When installing three or four memory modules, an error is generated in the BIOS that the modules dimm_c1 and dimm_c2 Failed\Disabled. At the same time, the memory in the dimm_a1 and dimm_b1 slots works correctly.
I tried to install ECC 2gb/8gb/16gb modules, all modules are working, tested on other servers.
Why only dimm_a1 and dimm_b1 work?
Who faced a similar problem?

Answer 1

mb should AA BB work, or enable the non-crossing mode in the BIOS

Answer 2

If the server is Rakovsky, then on the cover inside there is a diagram for connecting the RAM. Usually they don’t put three, they put in pairs