You are not alone. I've got the "iCloud can't find the page" problem as well.
Short summary: It seems that iPhoto/iCloud uses the same URL when you delete a Stream and then create a new one. The new one can then not be found.
Long story:
Also set up a shared stream yesterday for testing, got the invitation email, clicked the link, browsed the page successfully. All fine - not as nice or useful as MobileMe galery, but at last something that is again usable to share to my parents AppleTV.
- got rid of the first shared photo stream, confirmed the message the stream+files will be deleted
- checked on icloud.com (original share email), yep it's gone
- selected some images, clicked share, to PhotoStream, new
- readded emails of people to invite, renamed stream to Friends+Familly
- clicked on View website -> error message! ARRRGH!
- disabled and re-enable public website, click on View website -> error.
- called Apple Support: "Yes, some users are seeing problems, please try again later".
The link looks terribly familiar. Checked my Safari History. And yes it seems that iPhoto re-used the same link as for the original Photo Stream I deleted.
So:
- made a new Stream, check website -> works.
- remember URL
- delete Stream
- create a new one, check website -> broken.
Apple: We love you, but your quality control, arrgh! Especially when it comes to iCloud.