Looks like an older thread that got bumped back up - but just to add: they may have fixed the issue, or the site isn't being glitchy now, because I was booking for my 12/12 trip this morning and had no problem finding Le Cellier lunch and dinner availability for party of 2 on both Sat and Sun evenings.
I have occasionally had issues with the reservation system when booking for 1 and getting no availability, but switching to 2 usually works out. As Simba's Mom mentioned, when I show up solo I just notify my party is down to 1 and have never had an issue. I could see potentially an issue going from party of 4 to 2 or 1, since that often would change the table size...but 2 is the same table size.