Try this:Click the link at the line following File > Preferences > More preferences can be edited directly in the file. This will open the Arduino15 (or similar name) folder.Delete all files except preferences.txt. Please be very careful when deleting things on your computer. When in doubt back up!Tools > Board > Boards ManagerHopefully this time you will not encounter the verification failure.
Anything else I must follow to get rid of the issue http://arduino.esp8266.com/stable/package_esp8266com_index.json - Failed Verification.
Another cause of the JSON file verification problem might be your antivirus software. If the verification problem persists with the new installation try TEMPORARILY disabling your antivirus just long enough to run Boards Manager and check whether the problem goes away. If so, you will need to modify your antivirus settings to whitelist the file, process, or folder that's being blocked.Regarding the beta version of the Arduino IDE, it is intended for beta testing. There are some known new compilation bugs in the beta version, though they only happen in specific circumstances. When you encounter a strange problem (as you have) it definitely is worth checking to see if it's already been fixed in the beta IDE version, since there is always ongoing work to fix known bugs and make improvments, but you should be aware that you might also run into some new problems.I always use the beta version and have very few problems but the reason I use it is because I want to help the Arduino developers to find bugs so they don't end up sneaking into the production release. When I run into one of these bugs it's quite inconvenient but it also provides the opportunity to make a significant contribution to the Arduino project so it's worthwhile to me. For someone who isn't interested in participating in the development of the Arduino IDE and only wants working software I do not recommend using the hourly or beta versions unless there is a specific need for it.