• add new executable. See step1.png. "Add new executable" dlg. contains note: Path of the NAnt executable, e.g. c:\nant\bin\nant.exe
• Check that you have nant.exe in c:\nant\bin\. Copy there nant if not. Fill "Add new executable" dlg.
• Run a project plan where this nant job is used. See the log:
  Error occurred while running Task 'run nant(1)' of type com.atlassian.bamboo.plugin.dotnet:nant.
  13-Dec-2013 15:00:02 com.atlassian.bamboo.task.TaskException: Executable 'nant.exe' does not exist at path 'c:\nant\bin\nant.exe\bin\nant.exe'

• Type "C:\nant" as path to nant executable.
• Run the plan that contains this job.
  No error. nant is executed.

Please update the note " Path of the NAnt executable, e.g. c:\nant\bin\nant.exe" on the "Add new executable" dlg. or fix the behavior.