Did you make sure to install the RAM in slot 1 and 3, or 2 and 4? They should be staggered for correct pairing.
Yes
Slot 2and 4
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Run Rember which is a memory tester for Mac OS X....it will tell you if you have a bad stick. I had one in the Corsair Vengeance Kit for my Mac Mini Server...replaced it and all was well.
I just done full apple hardware test
A memory error was found.
Not sure it's because bad ram or compatible issue