When I get this issue sometimes, all I do is logout then login again then join the room I want.
Another thing try changing the captcha server under the Advanced tab in the Preferences.
I am trying it out for the first time today, as I finally decided to update to the newest Yahoo on my laptop here but am not able to log into a room. I set all preferences correctly, tried to log in and I do not get a captcha box to enter, I also went into preferences and changed captcha server and still nothing. It just sits there. Nothing happens. What else is there to try? If anything, please let me know. If nothing I am just going to revert back to the older version again and leave it as I never had a connection issue at all with it. Also, when I connect without YTK Pro it connects fine, but when I try to connect with YTK Pro it sits there and I also notice the icon for YTK Pro is not lit up in task bar so I take it it is not using YTK Pro cause I try to use the recently joined room side to connect to a room and it sits there and when I use the Join Room side that Yahoo gives so I can drop a room and select I connect to captcha with in room box that gets pulled up but I get spam bots messaging me and conference invites so that is how I know it is not connecting up with YTK Pro. I now need to get it hooked to YTK Pro, Yahoo that is, and I forget how to make it do it.