The American Express credit card can only be used to authorize and pay bookings with durations less than 100 days if the property is set up as a Lodging account (most BookingCenter customers are).   This is a technical limitation in the AX specification, as the 'duration' of a stay can only be 2 digits, ie 99 or less.  If the duration of a stay is 100 or more days, the authorization captured will always fail to settle and will not provide the monies from the card holder.

There are two work-arounds if you find yourself in this rare situation:

1. Break apart an extended stay duration booking into multiple bookings that are 99 days or less.
2. Pay the amex on a house account folio and then use a "transfer receipt type" to move the balance.  

Neither of these options are pretty, but are the only workarounds for extended stay hotels who accept AX.