The server lets channels know whether you connected with an SSL connection or not, and the channel has chosen to block people unless they do that.

Most networks have port 6667 as a regular non-secure connection.
When networks support a secure SSL connection, they usually tell the port numbers in the MOTD (message of the day) display you see at connection when you were connecting at 6667. The port number for that is often at 6697.

When you edit the serverlist entry to connect using the secure protocol, you should precede the port number with the "+", so where it currently has 6667 you should put in +6697 instead of just 6697. If you don't have the + there, it tries a normal connection at the secure port, and big fail.