The REAL Marriott reservation codes

[hantamouse.livejournal.com]

The code listed on the D*C website says DNPA, which causes an error.
My web browser helpfully suggested DGNDGNA and DRCDRCA, which must have been the codes I punched in for the last two years.
Well, there's an obvious pattern here. Educated guesses and experimentation revealed:

DNPDNPA - single/double
DNPDNPT - triple
DNPDNPQ - quad

I can't get a party room code to work.