And the problem returns (again)!
Novotel in Singapore does not offer Amex as an option when booking pre-paid rate.

Mercure in Laos does ... but, a short while after booking, the hotel sent me an email complaining that they couldn't get the card to work, and asked if I had another card.
I said "No" but asked if they could change my booking to the "Flexible" rate, so I could pay on arrival; I even offered to rebook at the flex rate. Nice people: they agreed to me paying on arrival, without increasing the charge to the flexible rate.

(I shall have other card options by the time I arrive in Vientiane, or I could even get a large sack full of kip from the 'bank down the road'!)
-- Henry