New user: error creating repository

[Timothy Reaves]

I just installed the latest Magma, and when I execute
MagmaRepositoryController
     create: '/Users/me/Development/magma/one'
     root: Dictionary new

I get a MessageNotUnderstood error.  Rijndael class>>asMakoEncryptable

Have I forgotten to do something?  I do believe I have created my key  
properly.