The error Memtest86+ shows signals that a bit was flipped by the memory when testing it, i.e., Memtest86+ set it to 1 and it was 0 when it read the value (or vice versa).
Problems with RAM are always serious, since flipping a bit in memory can cause pretty much everything to happen. The normal outcome is system instability, but with a little bad luck, you could also store a system critical file (or any other file that is important to you) in this part of the memory, modify it and overwrite the original file.
If you're overclocking the RAM, stop doing that. Take the modules out of the slots and re-seat them to be sure they're not loose. Run the test again and, if it fails once more, replace the defective RAM module.