ArcheAge is "evolving" its servers this week, and the servers today are being restarted to start prepping for this change. As such, the Auction House will be locked out until after the merge this week.
Gamigo announced the "server evolution" last month, giving players a timeline for when they expect to see the servers go down and which servers will be affected. The merge is planned for this Thursday, March 4th, with both EU and NA servers being brough down for the day to facilitate the merge. As such, today, the servers are being brought down to restart them in preparation for the merge.
However, when they come back online they will be without one key feature: the auction house will be locked out to prepare for the merge itself. The team states that two hours before the scheduled maintenance the AH will be locked out of creating new listings. The NA server will restart at 5am PT/8am ET, while the EU server will see its restart at 8am UTC.
The Server Evolution as it's being called is a merge of servers in ArcheAge and ArcheAge Unchained, aimed at merging the lower population servers together to form a new server that will see a population "roughly equal to each other." Scheduled for March 4th, the servers will be brought back online March 5th, though the team is cautioning that they will bring them back online one at a time in order to mitigate server queues and more.
You can check out the full server merge schedule, as well as see what your server will merge into, on the official post on the ArcheAge site.