The biggest problem with your script is that it's not formatted consistently. The second biggest is that you're using a checkbox instead of a button (I understand you want to 'challenge' yourself, but it's terrible to do that from a UI perspective).
Also note:
- There's no reason to hide every object since they're all children of the window. Feedback_Test_Window2.hide(); will suffice.
- There's no reason to send two triggers. Just send the value (whether they liked it or not) as a parameter.
- I'm not quite sure why you're using a server variable at all. Even if you do it with two triggers, a player. or player.clientr. variable would work fine.
- Make sure that the player has not already sent feedback on serverside to prevent hackers from voting infinite times.
- Not sure why you have sleep 100;, but that should be sleep(100);
- Give your GUI objects meaningful names. Feedback_Cancel is a better name than Feedback_Test_Button2.