I recently used a Marriott TravelCard to pay for a stay at the San Mateo Marriott. Lucky me, I was apparently the first one to use the card there under the new system. There was a scramble among the front desk employees, and they had to call for instructions and/or authorization. It took about 10 minutes total.

But thanks to this thread, I knew about the potential problem and allowed extra time in case it was an issue. Hopefully next time they'll know what to do, but from lkar's post, it sounds like they'll still need to call.