Cannot find photo stream details message - But I know it's a live and working Photo stream.

I'm trying to set up my Dad so he can view my photo stream.

I've got other people subscribed to my photo stream so I know it works.

I created an apple ID for him and have clicked on the "Subscribe to this photo stream" link in the invite email that he gets.

However when a new browser window comes up it displays the message

"Cannot find photo stream details"

Anybody know why this is happening and how to correct it?

Many thanks,

d