I am kindof puzzled over this, I have two free “promotion” days at Springhill in LasVegas; when I made the reservation I only did it for 1 king bed; within few days I tried to change it to two beds; ( my friend would like to join me) I was told there is no vacancy for two beds. However; a friend of mine (not a member) was able to get two beds for same days. I think as a loyal member and regardless whether if we are using a promotion or paying regular price, we should have the priority over non-member.
So what is the use of loyalty and membership in this case…?
It's difficult to speculate as to why you weren't able to change your room type, especially with it being over a holiday weekend. My suggestion would be to try contacting the hotel directly to see if A) They have the rooms with 2 Queen beds available B) Ask if you can switch your reservation from 1 King to 2 Queen.
FYI, just in case they're unable to make the switch for you: The room you currently have reserved has a sofabed, which might help accomodate your friend.