Any place is fine to ask questions... users have been good about forwarding us to where the conversation is happening.Tracking down info on the Duplicate Messge error is tricky: http://stackoverflow.com/questions/4874532/twitter-error-could-not-post-tweetI have not found it spelled out in the Twitter API, but it does exist.For example, if you send, "The temperature is 56" and "The temperature is 60" one message will likely get disregarded. You can even add time stamps or random numbers, and will still bounce - they have some matching detection. You are safe, I think every 3-4 hours if the content is the same.
If you keep the Serial Monitor window open on the Arduino sketch, you will see what gets reported back. That's where you might see Bad Gateway or a 403 error.