I cant lookup certain domain extensions. For example when I try to looup a .nl domain I get:
Your WhoIs query could not be executed:
You entered a domain name with extension .nl.
WhoIs queries on this domain type are unsupported.

Am I doing something wrong or is it just messed up?

It could be like the .orgs where you need to queiry the .org whois server (whois.publicinterestregistry.net) not the sponsoring registrar.

I believe whois results for .nl domains are returned by whois.domain-registry.nl regardless of what the sponsoring registrar was.

I use this place for .nl domains http://www.traceroute.nl/