memtest86+ crashing on server

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http://serverfault.com – we have a few DELL 1950 servers. 1 of this servers has CentOS6.3 and its randomly rebooting so I suspected it was hardware. (no log generated) the other 4 servers do not randomly reboot. We passed memtest86+ on the 5 servers, and on 3 of them memtest86+ crashes (displaying an odd and colorful screen, like if a video card failed) Although I tested old memtest86 (not +), and all servers did not crash. I also tested other RAM testers utilities, no tool failing. have any of you guys experience this? thanks (HowTos)