Design test - why does it not work?

Can someone shed some light on why the design test hasn't worked for any of my newsletters???

The email browsers are either stuck on "processing" (for over an hour) or there is a red "X" in the corner.

I understand that the newsletter can be rejected or classed as spam, but this newsletter only has a spam score of 0.6. Also, when previewing it manually by sending it to a hotmail address it isn't getting blocked.