Is the BTLC Down?
I rebooted my router and restarted the game, and it seems to be working again. Very strange as the rest of the game was working fine.
Sometimes this can help with issues like that without a restart:
1. Open your trading post
2. One your options panel
3. Change the language to French
4. Wait for the trading post to reload in French
5. Change the language back to English (anglais)
6. Test trading post
Other times, a client restart is absolutely needed.
Please post back if you get to try this and whether it works or not.