Elixir - OpenSSL might not be installed on this system.

Does this look like a familiar error message?

10:51:54.415 [error] Unable to load crypto library. Failed with error:
":load, Library load-call unsuccessful."
OpenSSL might not be installed on this system.

** (UndefinedFunctionError) undefined function :crypto.strong_rand_bytes/1 (module :crypto is not available)

10:51:54.423 [warn]  The on_load function for module crypto returned {:error, {:load, 'Library load-call unsuccessful.'}

This happened after I ran iex -S mix on an Elixir application to which I added the uuid package.

After some searching I was able to verify that this is not a problem with erlang by running:

$ erl
Erlang/OTP 18 [erts-7.2.1] [source] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false] [dtrace]

Eshell V7.2.1  (abort with ^G)
1> crypto:strong_rand_bytes(16).
<<5,109,149,68,194,186,34,79,49,211,157,89,232,77,149,105>>

The solution? Deleting my _build directory and compiling it again worked the first time iex -S mix was run, but subsequent runs would break it again. The ultimate solution? Re-install Erlang.