Forums Connection Issues "#channelname Cannot send to channel" why?

You can't send messages to a channel if:

a) The channel is moderated (mode +m) and you have not been given voice privleges (user mode +v)

or...

b) You were banned in the channel but not kicked out.

As for the nick registration, different networks have different nick registration services. Try channel #help or something similar and they should be able to tell you how.