On the 9th October 2012 Twitter stopped the implementation of the RSS feed for your twitter timeline.
So if you are using the old url which looks like this
where USER_ID.rss represent your twitter userid, then you need to switch over to the new method. Which looks like this
where YOURUSERNAME represents your twitter username. So for Zone1creative this would be https://api.twitter.com/1/statuses/user_timeline.rss?screen_name=zone1creative
However, you should should know that twitter will be stopping this method in March 2013 too. So you will need to find out an alternative method for next year
For more information : https://dev.twitter.com/docs/api/1/get/statuses/user_timeline