You've probably bought the wrong model of modules for that Tyan motherboard. The TWINX kit is part of the XMS series, which requires a higher than JEDEC-standard voltage in order to work reliably at the advertised timings. Unfortunately, Tyan offers no provision at all whatsoever to adjust the memory (DIMM) voltage on their motherboards.

In other words, you've bought the correct type of memory (registered ECC), but the wrong line. And the Socket 940 Opterons will not work at all with unbuffered memory (ECC or non-ECC) because it requires registered memory.

The only 1GB DDR400 Corsair module which will work with your motherboard is the CM72SD1024RLP-3200 module.