When going to TradeMe for around the last 15 minutes I've been served up the following error:

https://www.trademe.co.nz/
Error: Server Error
The server encountered an error and could not complete your request.
Please try again in 30 seconds.

Interestingly I can re-use a bookmarked URL to do an expired listing search.  Trade Me - New Zealand Online Auctions and Classifieds

Knowing little about complex web design and hosting, I'll speculate wildly that it's a back-end database issue and the live database has a fault but the database that expired listings are moved to is working fine.