My guess turned out to be correct. It was the HTTPS prefix.

I took the prefix out when I copied the URL at their site, put it in the box and it worked.

Fixed.

Could be the link length...but Wayne once told me there was more than enough room.

Could be the 'HTTPS' secure prefix since the page feature was made for the site before its common use, but that's illogical.

Since the link actually works from the comments, but not the yellow box, it's reasonably safe to assume it's a page function bug. One more thing to add to the fix list when Wayne gets some time to sort these things out.

Until then, a working link is on the page, so it's all mostly good. He can deal with the rest.