Crucial's maximum memory differs from Apples recommendation
We test our memory in systems to guarantee compatibility and we do sometimes recommend more memory than your manufacturer does. We only recommend more memory against a system if it has been tested and is guaranteed to work.
Always make sure you are looking up the correct version of your Mac before ordering. You can do this by running the Crucial System Scanner or by checking your processor type and speed, screen size and memory speed in About this Mac... and selecting the relevant model from the Memory Advisor tool
If you have ordered memory and it’s still not allowing the system to boot please follow the steps from this page System won't start after memory upgrade and if there is a fault or issue please let us know.