This is a common issue with both early and late 2011 MacBook Pros. I read somewhere that this issue is caused by a failure on the motherboard. I believe Louis Rossmann pointed this out (New York based fixer and YouTube poster - https://www.youtube.com/channel/UCl2mFZo...). It only stops SSDs and not HDs being used internally. I don’t know if Samsung or Kingston SSDs are useless in the the 2011 MacBook Pro so if anyone out there has had the problem with Crucial but not other SSDs please post and let us know.