Why does Scala fail to instantiate a Companion Object?

I am new to Scala and Akka so forgive me if this is a newb question, but I can't find the answer anywhere else...

For the record I am using Scala 2.9.0-1 and Akka 1.1.3 and have included my SBT 0.10.1 setup as well.

I have written the code that follows this message as an experiment in Akka; it is a toy version of a user database and registration facilities. The basic idea is there is an ActorPool of UserServer actors each of which have an instance of a MemoryUserDatabase which uses STM to interact with a Map of Users keyed off the users' email addresses - pretty simple, right?

The problem can be reproduced by compiling the file and running the following in two separate consoles:

Console #1:

import toy.service.user._; ServiceRunner.run

Console #2:

import toy.service.user._; ClientRunner.run

This is the output from the server console (#1)

Aug 31, 2011 5:21:29 PM org.multiverse.api.GlobalStmInstance <clinit>
INFO: Initializing GlobalStmInstance using factoryMethod 'org.multiverse.stms.alpha.AlphaStm.createFast'.
Aug 31, 2011 5:21:29 PM org.multiverse.stms.alpha.AlphaStm <init>
INFO: Created a new AlphaStm instance
Aug 31, 2011 5:21:29 PM org.multiverse.api.GlobalStmInstance <clinit>
INFO: Successfully initialized GlobalStmInstance using factoryMethod 'org.multiverse.stms.alpha.AlphaStm.createFast'.
[ERROR]   [8/31/11 5:21 PM] [akka:event-driven:dispatcher:global-3] [LocalActorRef] Availability(foo)
java.lang.NoClassDefFoundError: Could not initialize class toy.service.user.memory.MemoryUserDatabase$
    at toy.service.user.memory.MemoryUserDatabase$$anonfun$getUser$1.apply(Registration.scala:96)
    at toy.service.user.memory.MemoryUserDatabase$$anonfun$getUser$1.apply(Registration.scala:96)
    at toy.service.user.memory.MemoryUserDatabase$$anonfun$getUser$2.apply(Registration.scala:96)
    at toy.service.