you have (2x2GB) meaning two memory dimms.
When you get memory errors pull one of the dimms and retest. If it passes, take the good one out and put the other one back in. If it fails return it for exchange. if they both work fine as the only memory dimm then try them both together again. Sometimes re-seating the memory fixes the problem.
Good call fun500 on the memory test.
p.s. you are hoping that the memory was bad given that the memory test failed. The other options are bad bios setting for voltage/speed (force them manually, do not let the MB bios detect your memory speed especially with low voltage or high performance memory) or something else bad that is seen as a memory test error (MB, bad card in pci slot, etc.) Memory is about the cheapest problem you can have.