Hi Dennis,
That is pretty strange... How did you trigger the action/task when testing with the analyser? When using the 'Execute' button it will indeed send the command twice. Once when pressing the button, and once when releasing it.
You can trigger it manually only once, but it is a bit silly. You will have to make an action in the actionlist 'OSC', and put the triggerflank on 'Down'. Now you can add the task 'Action - Link - Set' and set parameter1 to execute your action which contains the RS232 message. Now you can press the execute button on the action (not on the task! You really have to select the action in the Showcontrol homepage and press execute there)
Normally your action is triggered via something else then the Execute button. You can then use the trigger flank if needed to make sure it triggers once. Depending on what triggers it. Most cases it will only trigger once anyway, unless your trigger sends an off value when released.
I hope this makes sense... Let me know if triggering it once instead of twice makes the difference.
Greetings,
Bootsy