I have installed good memory sticks, from another computer, that works well. All show up as good memory, no N/A.
I then install my questionable memory back. This time I swapped A1-A2 & B1-B2 for C1-C2 & D1-D2. In other words, I swapped the position of the 1st 4 sticks with the last 4 sticks. This time the last 4 sticks, C1-C2 & D1-D2 were shown as N/A.
Previously it was B1-B2 that was shown as N/A.
Bob