Memory Error Detected!

A number was written to memory, and when that same location was read back after some delay, a different number was found.

This is not normal. Your RAM is bad, or your system is incorrectly configured. Even just one error means that you have a problem. If you have overclocked your machine, or selected aggressive RAM timings in your BIOS you should try more conservative settings before judging the RAM fully bad. If you can't get MemTest to run without errors even with conservative BIOS settings, however, your RAM is the most likely cause. Correctly functioning RAM has no errors, even if you run MemTest for days. 

Read the manual for more details on how to determine the exact source of the problem.