diff --git a/script/RobotTCP.py b/script/RobotTCP.py
index 809c84f..b2f924f 100644
--- a/script/RobotTCP.py
+++ b/script/RobotTCP.py
@@ -380,14 +380,14 @@ class RobotTCP(TcpDevice, Stoppable):
     #High-level, exclusive motion task.
     def start_task(self, program, *args,  **kwargs):
         for task in (self.high_level_tasks + [program]):
-            if self.get_task_status(task)[0]>=0:
+            if (task is not None) and (self.get_task_status(task)[0]>=0):
                 raise Exception("Ongoing high-level task: " + task)
         self.current_task = program
         self.task_create(program, *args, **kwargs)
 
     def stop_task(self):
-        for task in (self.high_level_tasks + [program]):
-            if self.get_task_status(task)[0]>=0:
+        for task in (self.high_level_tasks + [current_task]):
+            if (task is not None) and (self.get_task_status(task)[0]>=0):
                 self.task_kill(task)
 
     def on_event(self,ev):