Danny Jordan
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I'm using a MacBook Pro with OS X Sierra and it isn't a fix but I was able to rebind mine by holding the function key, then clicking the button I wanted to remap, and while still holding the function key pressing the desired f# key. it worked for rebinding with me at least. As I have said though not a solution but a workaround to achieve the desired result,
This is not the place to ask for help. This is for reporting bugs. You have also not supplied sufficient information. Such as java version or computer specs.
Did you try restarting your computer? Sounds like it is your problem not Mojang. The directory that it saves files to is locked because something else on your computer is accessing it. Usually a restart will fix that.
Also it is rude to come to a bug tracker and tell devs to "FIX IT".