Looks like this affects all installations of Arduino for Mac, Windows, and Linux. The next build of Arduino will address this, but for the time being, the fix is below:
We had a problem on our package_index.json that caused the error and prevented the IDE to start.
Now the package_index has been fixed, but to recover a working installation you must delete once again the package_index.json with the cache folder and restart the IDE as usual.
- remove file C:\Users\YourUsername\AppData\Local\Arduino15\package_index.json
- remove folder C:\Users\YourUsername\AppData\Local\Arduino15\cache
- remove file /Users/YourUsername/Library/Arduino15/package_index.json
- remove folder /Users/YourUsername/Library/Arduino15/cache
- remove file /home/YourUsername/.arduino15/package_index.json
- remove folder /home/YourUsername/.arduino15/cache
Please note that the problem that prevents the IDE to start has already been fixed and it’s ready for the next release, that’s the reason why the Nightly/Beta Builds are not affected, and also the reason why we did not detect this problem earlier, sorry about that!
Solution source here