Go to "My Account" (top right of screen) then select "Edit Profile" - the EMail field is there as "Real Email:" with the link for the birthday screen underneath it.
You may just need to ensure an EMail address is entered before dealing with the birthday.
If you try this yet still get an error, and are sure that the address you're entering is valid, please PM me with the details and we'll check it out for you.
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Giraffe: a ruminant with a view.