RSS feed is having problem, but I can't tell what's wrong

I have created an one-item RSS feed which has been used on one of my non-WP site successfully. But it is not working on my WP project: To test various RSS feed, I tried 3 different widgets. The results of these 3 are here: under the header picture, on the right-hand side.

When I entered the URL to the RSS widgets, Super RSS Reader accepted the URL, but displayed an error message. For the other two, they complained when I entered URL (the same error message as “Super RSS Reader” is displaying). After I forced, they displayed nothing.

The RSS file is here.

To be sure that there are some problem with my RSS file, I also created a fourth Widget with CNN’s feed, it worked nicely.

Although the error message is about “not valid URL”, I suspect that the complain might be about the content.

My question:
1. Do you see anything wrong in my RSS file?

2. Are there any tools which can pinpoint to me what’s wrong? I tried “RSS validator” plugin, but it only validates feeds from WP, not external ones.

Thanks

John Zhu