Similar thing happened to me two days ago, although I was booking cash + points reward rooms. Tried four times for the first room. The first three times, it "could not complete the reservation". I finally got my first room. I tried several more times, and I also got my second room, or so I thought.

However, when I checked my accounts, I was charged three times on my credit card, received only two sets of points on my Priority account, and only one room showed up as reserved!! Called customer service, and was told that the second room was no longer available. The points would be reversed on my Priority account, but I now have to wait for the credits to appear on my credit card, and I have one room booked which is useless without the second!!

I reached Platinum status with IHG for the first time this year, and hoped for better service than this.