Domains not resolving anymore for some people.

This is so weird... All of a sudden, some people aren't able to  
resolve domains.

Could someone check if hecht-co.nl resolves?

All the steps as described on "Checking addresses of your computers"  
succeed, yet some people are saying the address doesn't resolve.

I'm at a loss at how to proceed.

[1] http://cr.yp.to/djbdns/run-server.html

-- 
Regards, Charles.