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);
}