Tried to get the best of both worlds, HELP

[Saiminjutsu]

Ok, so i knew of another free to play realm that i could play on that went higher than Vanilla, Ash Realms. Maybe some of you are familiar? But anyways, did that and it updated Vanilla pretty much although i had heard you could have multiple instances of WoW on your computer. Well i went to go uninstall it and now it says ""Unistall.xml" could not be read". I just want Vanilla back T__T pls halp.

[AverageJoe]

If you connected to another realm and they did anything to your client once you connected (Patched, updated, etc.), you'll need to reinstall a fresh 1.12.1 vanilla client again as non-1.12.1 client or modified clients get kicked here on Nostalrius.

Follow the steps in this thread to download and install a fresh 1.12.1 client:
https://forum.nostalrius.org/viewtopic.php?f=32&t=638