Created Unassigned: RegisterChanges Method Exception - account name [12225]

I'm attempting to use the TaskService library (because it offers some functionality missing in the native PoweShell cmdlets for Scheduled Jobs) to update a scheduled task with a 'Zero' timespan which should disable the 'Stop the task if it runs longer than' setting however when I call the 'RegisterChanges' method I get the following exception:

Exception calling "RegisterChanges" with "0" argument(s): "The name provided is not a properly formed account name."
...
+ $task.RegisterChanges()
+ ~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : SecurityException

Any ideas? Given the error message I've tried updating the scheduled task with the Library using both a local admin account and with a domain account that has local admin rights on both a Windows 7 Desktop and a Windows Server 2008 R2 system but I get the same exception in both environments for both accounts.

Thanks in advance,

Ryan