When my build job starts I get this Console Output (I have sanitized some doman names and replaced my job name with "myjob":

Started by timer
Building remotely on Worms_IOS
Reverting <sanitized>
Updating https://<sanitized>
At revision 66
no change for <sanitized> since the previous build
No emails were triggered.
Working directory is /Users/builder/workspace/<myjob>.
[<myjob>] $ /usr/bin/xcodebuild -version
Xcode 4.2
Build version 4C199
Fetching marketing version number (CFBundleShortVersionString) from project.
[myjob] $ /usr/bin/agvtool mvers -terse1
FATAL: java.lang.String.isEmpty()Z
java.lang.NoSuchMethodError: java.lang.String.isEmpty()Z
at au.com.rayh.XCodeBuilder.perform(XCodeBuilder.java:195)
at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:19)
at hudson.model.AbstractBuild$AbstractRunner.perform(AbstractBuild.java:695)
at hudson.model.Build$RunnerImpl.build(Build.java:178)
at hudson.model.Build$RunnerImpl.doRun(Build.java:139)
at hudson.model.AbstractBuild$AbstractRunner.run(AbstractBuild.java:461)
at hudson.model.Run.run(Run.java:1404)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:230)

Let me add that when I run agvtool mvers -terse1 from the command line in that working directory it displays "1.0".
Here is my java info for the slave:
worms:~ builder$ java -version
java version "1.6.0_29"
Java(TM) SE Runtime Environment (build 1.6.0_29-b11-402-10M3527)
Java HotSpot(TM) 64-Bit Server VM (build 20.4-b02-402, mixed mode)