Hilton HHonors - Special offer for London, but no availability?

I just got an email from the bank that issues my HHonors credit card (DKB, Germany) with a special offer for The Trafalgar in London, informing me that if I use promo code PR20EW, I'll get the sunday night for free when booking a friday and a saturday night. Trying to use the link they provide, I see that there's no availability on any day for that code. Trying to book with the code from my HHonors account page, I only get an error message. Does anyone know about this code or has ever successfully made use of it?

Tried plugging in various dates and doesn't seem to work online. Try calling them to see if you can reserve it on the phone and let them know about the unavailability online.

Here's betting the rates for Fri/Sat night will make the normal rate for Fri-Mon basically the same :D.

If you are trying any dates in July / August, they have probably got no availability due to the Olympics -- all rooms full, all rates thru the roof, all promos opted-out of for the duration etc., etc.