There are several things that might prevent you from joining a particular channel. In most cases the server will tell you the reason, but some clients do not correctly display that information to you, so it's useful to be able to check for yourself. Some of the common causes, in no particular order, are:
- Check that you're logged in with services. You can log in by running
/msg NickServ IDENTIFY YourNickname YourPassword. Some channels use mode
+R, which prevents unregistered users, or users who aren't logged in, from joining.
- Check whether the channel has modes
+kset. These will prevent anyone from joining who isn't explicitly invited or doesn't know the channel password.
- Check whether mode
+jis set. This is a join throttle, which prevents lots of users from joining in a short period of time. If this is the case, it might be worth trying again after a minute or two, to see whether the join throttle is the reason.
- If you are logged in to services, check the channel ban list -- you can do this using
/mode #channel b.
If you've not been in the channel in question recently, it's possible that you're affected by a wide-ranging ban, so pay attention to any bans that include
? wildcards. Some bans may be extended ban types; you can see more information about these here.
If you find a ban which matches you but you feel wasn't intended to keep you out, then talk to one of the channel operators to see about having it removed.
If you're still stuck, feel free to ask a staff member for help in working out what's preventing you from joining.
The two most common causes for this are either a mute ban -- use
/mode #channel b to see the list, look for bans starting with
m: and then check the advice above regarding bans -- or mode
+m, which prevents anyone who isn't voiced from talking. The channel may also be set to mode
+M, which prevents unregistered users from talking. If you're still unsure, again, feel free to ask staff for help in working out what the problem might be.