I got the Phantom offer too, but my account was supposed to be just one night short to maintain Gold and I was already "comped" to keep my Gold status until 2011. I also got the error message but then later on yesterday this phantom offer disappeared.
I immediately logged on my husband's account, who is also Gold until end of this month, and he only had 3 nights paid stay last year. He did not get the Phantom offer when mine was still "alive". So it appears that this offer was only good if the account is within a small amount of nights stay to maintain Gold.