Freshly generated single player world, freshly generated files for InventoryTweaks. Still does not work. Using the latest build of forge or even 1025. I did not add anything to the sorting rules file. I simply opened it and pressed ctrl s to save it, though nothing was added. Pressed R in-game, and that error pops up. No other mods were loaded at that time either.

Are you sure there's no message before that? There seems to be a strange case displaying that message when creating the default files fails, that matches the format in the picture better than the actual invalid keywords error.

Yep. That's the only message that comes up. Pretty sure its also what is causing the sorting to not work properly.

Are there actually invalid keywords in the Tree file? I am unable to sort anything on my inventory as well, even when Rules are set. I'm not sure if that has anything to do with the Invalid Keywords error.

Another problem. Opened up the Rules file, press ctrl S again, pressed R in-game. Gave that message. Opened up the Rules file again, pressed ctrl s again, press R in-game again, and it gave that message. This is with the 106 build. It's as if it thinks its missing, but it really isn't.

It's not having an issue with the rules file so messing with that shouldn't be doing anything.

Try deleting the InvTweaksTree.txt file and see if making it actually re-extract that helps.

Deleted it. Let it regenerate a new one. Pressing R did not show the error at first, opened up the sorting file, did the usual ctrl s and pressed R again. Displayed the same error.

Well, I have no idea then. Nothing you do to the other file should be changing that one. Try using a different text editor?

Just wanted to let you know that I used another text editor, same problem.

I found what was causing this there, it thought the tree file was out of date so kept trying to replace it.