Well, I have the same problem. The file isn’t large and it’s in my own server so it isn’t down.
The funny thing is that I can actually open the file by clicking the link embedded in “here” in the error message. So now the question should be how to skip the error message and make GDE/Google Viewer show the file right away.
If the error is exactly the same as the one reported by kepongcoder, then there is nothing I can do. The service itself is not working for your document for reasons unknown. I may be able to make some suggestions but I’d need a link or something idenfifying the problem document (you can use the Support link at the bottom of the GDE Settings page)