It's bad usability because the visitor is presented with a page which has no information, no visual clues as to whether this is normal or not, no navigation elsewhere, nothing. If you think a blank page has nothing to do with usability, then I think you really need to go read up on the subject.

Having an appropriate error message would help, along with links to suitable places to go next. Never having to see that error message would be a better way to go.

P.S. Wildhoney confused me, I saw the avatar and thought I'd posted something without remembering typing it!