If your RSS feed stops updating and you are using Feedburner, it’s likely that your feed size has become too large. Feedburner stops updating feeds when the size of your original feed is larger than 512 KB.
This video shows you how to check the size of your Feedburner feed so that you can avoid having your feed interrupted. Once your feed size goes back to being less than 512 KB’s, Feedburner will continue to update and deliver your RSS feed to your subscribers.
You can also reduce the amount of items in your feed to help prevent feed interruptions.
Check your feed’s size at Web-sniffer.net.