A few issues I've run into will dialog is that Facebook tries to fill in any missing data. So if you don't provide a description and caption, Facebook will try to scrape the page to get that content. Depending on how the page responds to the "scraping" Facebook will error out. I always make sure I include at least a space for those fields.
It seems the feed url you provided is similar to what is in the documentation. But the demo in the documentation has extra parameters.I'm about to add page support to my Facebook app, which does the same thing as yours. http://apps.facebook.com/countdown-timer/
