No, it was not a simple case of deactivation, the system was broken.
I tested my own promo-codes and they were being shown as INVALID. Also, as I said above, for a period of time existing promo codes were not being shown in the rewards section of the Web Panel.
I contacted DreamHost, as I have in the past when the promo system was not working, and they confirmed that the problem existed.
Anyway, the problem does not seem to have re-occured since, lets hope they fixed it for good. Also, the services downtime scheduled for tonight (now actually:) might be related, maybe they are replacing faulty equipment.
Save [color=#CC0000][b]$50[/b][/color] on DreamHost hosting using promo code [color=#CC0000][b]SAVEMONEY[/b][/color] ( Click for details )