I am glad someone else is having this issue. At least I know now that it is not something specific to my system and it will get a little more priority in support.
There is a registry key that you can export that contains all the channel configuration you enter. If memory serves it is located at HKEY_CURRENT_USER\Software\JRiver\Media Jukebox\Properties\TV Channels. Just export that key and keep it somewhere safe. Then, if you lose the channel settings you can always re-import it.
As far as the DLL file, you have to install version 9.1.262, it contains a file called MJTVControl.DLL that is at version 3.2.205.0. Save that file to someplace safe, and then re-install 9.1.274. Then overwrite the newer MJTVControl.DLL file with the one you saved from the previous install. Test out the channel scanning again and it should work fine with the older DLL file.
You should send a message to Yaobing, referring to this post, to let him know that you are having the same issue. I spoke with him last week, and he was looking into the issue but I haven't heard back from him yet.