There are enough problems with Crucial being discussed in this forum, including my own experience, that is seems "crazy" to me to take the chance with Crucial, especially when there are other brands out there, namely OWC, that are presenting NO fitment problems.
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I have no doubt that some are not having any issues with the Crucial product, but others are. In my case, I can say with certainty that my problem had nothing to do with not knowing how to use the folding RAM slots correctly. The DIMM's just simply do not fit properly. I can compare, side by side, the fitment of the Crucial RAM to the factory Apple RAM and the OWC. Both the Apple and OWC fit perfectly with no issues.
Can you post pictures of the Ram side by side and the memory slots. I'm surprised that you didn't do this already.