Recently I have started trying to run a dedicated server. At first I followed a tutorial and it was working fine. So I changed a few things in the init.txt, and the next day no one could join. Now whenever someone tries to join the log says:

2011-10-01 15:23:46 JOIN SUCCESS "playername" player 2 machine 2 (71.237.51.119:2303) cdkey ************************
2011-10-01 15:23:46 TEAMS JOIN " playername " player 2 team 1
2011-10-01 15:23:48 QUIT <No Player> machine 2 (71.237.51.119:2303)

I don’t remember what all I changed, but I know I enabled the logs. I even tried undoing what I did and following the tutorial exactly again, but it did not work. Does anyone know what the problem could be?

Don't you need to run the Dedicated server on one PC, Then play on it on another PC?

Or I think You can Do both on one PC, Though I think You'll need a pretty Powerful Machine :P

I don't understand what you are saying here. It sounds like you are saying I have to be in the server for anyone else to be able to join. If that is what you are saying then, according to the log someone tried to join while I was in the server and could not.

What he is saying, is that you should be running the dedicated server on one PC, and not playing Halo CE on that same PC at the same time so that you do not lag out the players in the dedi. You do not need to be in the dedi for others to join. If you do want to join your own server, use another computer that has Halo CE instead.

Now, back to your problem. Could you post the init.txt you used for your dedi server, as well as the addons (ie. Gandanur or SAPP etc) you are using for your dedi server?
Also, check if:
Your server is set to public.
Your firewall has an exception for the dedi server's .exe, and you have forwarded your dedi's ports properly on your router/modem/whatever you are using that links your dedi server's computer to the internet.

For more information:
This is why you shouldn't run your dedi server and Halo CE on the same PC
http://hce.halomaps.org/index.cfm?nid=239

These are the ports you should open in your router (and firewall, if the firewall on your dedi server's PC uses port-based blocking rather than program-based blocking). This assumes you did not change the ports your want the dedi to run on.
http://hce.halomaps.org/index.cfm?nid=237

Ok, to clarify I am not running the dedicated server with the same PC as the one I am playing on.

I am only using init.txt and a motd.txt for my server. The init.txt is:

sv_name "Ambush dedicated"
sv_motd motd.txt
sv_public 1
sv_maxplayers 10
sv_mapcycle_timeout 15
sv_friendly_fire 1
;sv_password ""
sv_log_file haloserver
sv_log_enabled 1
sv_log_rotation_threshold 500
sv_log_echo_chat 1
;sv_tk_ban 3
;sv_tk_grace 3s
;sv_tk_cooldown 5m
;sv_tk_penalty 1h 1d 7d
sv_map Ambush "ctf"
sv_timelimit 40

I have all the exceptions in my firewall, and I believe my router is set up correctly. What I don't understand is how I had a few people join before, but not anymore.

I think I see where the problem is.
Change your init.txt contents to:

sv_name "Ambush dedicated"
sv_motd motd.txt
sv_public 1
sv_maxplayers 10
sv_mapcycle_timeout 15
sv_friendly_fire 1
sv_password ""
sv_log_file haloserver
sv_log_enabled 1
sv_log_rotation_threshold 500
sv_log_echo_chat 1
sv_banlist_file h18fn1
sv_tk_ban 3
sv_tk_grace 3s
sv_tk_cooldown 5m
sv_tk_penalty 1h 1d 7d
sv_mapcycle_add Ambush ctf
sv_mapcycle_begin

Always:
1. Have the sv_mapcycle_add and sv_mapcycle_begin at the end of the init.txt
2. Specify a sv_banlist_file if you want to have the sv_tk options enabled. h18fn1 is the banlist file in this case, and by default it should be in your My Documents/Halo CE folder.

And one last thing: if people seem to not join your server, it could be because they do not have the map that your server is running. Its okay if that happens.
Also, people may join and get an error like the one in your log file in the original post, because they do not have the map and yet attempt to join.

Otherwise, there should be no problem.

Thanks, that seems to be working. I still have a few people failing to join, but I have experience that myself when trying to join some servers. BTW, any one know how to make a server message repeat automatically every so many minutes?