Several Windows Azure users have been complaining about two errors that show up when they click on a bill in account.windowsazure.com:
1 - Resource not available
2 - The requested PDF document is not yet generated
The Windows Azure billing system does not generate a bill if you do not have any charges in a billing period. However, the billing UI still shows links to bills for every billing period. So, clicking on one of these links will lead to either of the above errors. We are working to fix this problem, but until this issue is fixed, keep in mind that clicking on links with $0.00 next to them will show you an error.
If you feel that you are getting this error for some other reason, let me know at baslam at microsoft dot com - I will be happy to help you out!