First, are you in the channel? If your trying to send a message from outside the channel, the no external messages may be on. Second, is the channel moderated, and are you without a voice? If there is +m, and you are not voices, you can't talk. Also, on some servers, the ban of address 1 (no kick) on a channel is a "mute" ban. Basically, while the ban is in effect, the banned user may not speak.