It looks like these can only be ordered one at a time if I understand the package config column in the link you provided to me. This might be the problem. The part WA133UX6G8 is probably the one you should have purchased. You could still have a motherboard issue -- it is hard to tell at this point.
The modules in a Tri-channel (or dual-channel) kit have been selected such that the modules work together well. One module may be just a little more (or less) sensitive than the other which causes the module to not work well with another. I don't know if it would be possible to loosen up the timing to fix this or not. You would have to configure your system with one module installed and then install the other modules. If you are going this route I would ensure you run memory tests and stress tests.