Memtest86 is a program designed to stress-test your systems memory. You would use this test to verify the stability of your system's RAM. If it crashes durring this test but not under normal usage, you could disregard it as a bug; however, you are having trouble with your system, prompting you to run this test, the test also fails. To me it is clear that you cannot trust that your RAM is stable.
Try removing all RAM except for 1 module and run the test again, if it passes add more back into the system, if it fails try another module and set the failed one aside. Repeat this until all RAM has been added or set aside, then you will have a good idea of which module(s) are bad.
Running a stress test on a suspicious system and disregarding a failed test as a bug is the same as going to the doctor for a cough and disregarding his diagnosis of strep throat. You are running the test to find what is wrong, trust the results.