public sealed class ExportTaskException : TaskException, System.Runtime.Serialization.ISerializable  

{
  // get the first project task item
  var taskItem = Project.Current.GetItems<TaskProjectItem>().FirstOrDefault();
  // if there isn't a project task item, return
  if (taskItem == null)
    return;

  try
  {
    // export the task item to the c:\Temp folder
    string exportFolder = @"c:\temp";
    //At 2.x -
    //string fileName = await TaskAssistantModule.ExportTaskAsync(taskItem.TaskItemGuid, exportFolder);
    string fileName = await TaskAssistantFactory.Instance.ExportTaskItemAsync(taskItem.TaskItemGuid, exportFolder);
    ArcGIS.Desktop.Framework.Dialogs.MessageBox.Show("Task saved to " + fileName);
  }
  catch (ExportTaskException e)
  {
    ArcGIS.Desktop.Framework.Dialogs.MessageBox.Show("Error saving task " + e.Message);
  }
}