I found a workaround, I "rented" the game on the library computer, and copied ONLY the mods/core folder, cause that is what the editor needs to work, and it worked. Made a new folder in the rimworld folder and put the editor and the "rented" mods/core folder and it works again
No clue why it stopped working before. I compared the "rented" mods/core folder and my steam copy's mods/core folder files and they are the same. All I know is it's working with my little trick. If you are wondering if I kept the "rented" copy of the game I did not, I only kept the mods/core folder, nothing else.
It wasn't the save file causing the error, I can't figure out what caused it but I have 8 errors from my attempts to get the program working logged in my event viewer in Windows 7 64bit
If I do ever figure out what caused the problem I'll be sure to write down step by step what I did to reproduce the issue