Ah, it was G. Removing G may yield a result. Why the system wouldn't just ignore G if not available is beyond my understanding.

Some searches result in an error message that does not pertain to anything specific on the page. Trying again and again with the very same data helps.

Also, the booking page sometimes messes up the date that I choose from the calender and reports an error. The booking system somehow likes to switch month and date and then stumble over that. Hilarious.

Sometimes I can get a valid result now. Thank you. :-)

BTW: Anyone here know if there is any difference in fare rules between S and T?