Arduino IDE 1.8.6 not starting.
The cause of the problem is that you have a corrupted library index file. The solution is to delete the file, which will force the Arduino IDE to download a (hopefully) uncorrupted fresh version from the Internet:


Open the C:\Users\JK\AppData\Local\Arduino15 folder
Delete the file library_index.json
Try starting the Arduino IDE again




For anyone encountering this problem who is using an operating system other than Windows, the location of library_index.json is different:

On Linux:

/home/{username}/.arduino15 (a.k.a. ~/.arduino15)

On macOS:

/Users/{username}/Library/Arduino15

If using the Arduino IDE in portable mode:

{Arduino IDE installation folder}/portable



The issue of a corrupted library index file preventing the Arduino IDE from starting has been reported to the Arduino developers and they are already working on a fix:

https://github.com/arduino/Arduino/issues/7937