No such nickname online
When I try and type, I get this message:
TheChannelName: No such nickname online
And other variations on the theme. Further, there is no one listed in the channel.
The reason is in the message. Channel names begin with the character #, so by example, when you entered the channel name in the Mibbit Home tab,
is what you wanted to type.
What actually happened in the background, is you started a PM with a nick called TheChannelName, and when you typed, there was no person online with the nickname of TheChannelName.
Yes, there are other characters indicating different channel types on different IRCd systems and different networks, but # is by far the most common character that the new user requires.