White-Tiger and the other officials have no mods to download, so this message appearing is worrying. I'd suggest to remove the whole Strange Loop Games folder in AppData/LocalLow and trying again. (It's a hidden folder in your user folder, you might need to change Windows settings to see it)
If that doesn't work, an additional full uninstall and reinstall would be the next thing to try. This likely is caused by mods and unfortunately we do not offer support for modded clients, but the nuclear solution should work in any case.