12th Feb 2008 - it worked for me ... but I had to lie a little bit
Initially she told me I had to call the Ryan Air hotline but after I said I had been on-line for a while and came through here she said she would look into it for me.
Seems you need a Ryan Air reference no to book the Stansted Express thru the Ryan Air website - which didn't seem to like my credit card. The website remembers the booking, even if it failed for up to 30 or 40 minutes, which is incredibly annoying.
EXTRA INFO: The woman I spoke to could not create a new booking over the phone, but she was able to see whether I had a booking or not by using the Ryan Air reference number you enter when you attempt to make the Stansted Express booking. Have this handy when you call, it can be found in your Ryan Air confirmation email and is usually 6 digits.