I'm beginning to see quite a few nicks on IRCnet that are over 9 characters long, has the limit changed recently?
Indeed, from 9 to 15. Some servers have not been upgraded yet.
It's causing problems because I can't send messages from mIRC 6.16 to people with long nicks
I just tested this, by sending a message from a short nick on a server with NICKLEN=9 to a long nick on a server with NICKLEN=15, using mIRC 6.16, and it worked just fine - so there must be another explanation for your problem...