Does it say which file is the one with the CRC mismatch?
Which operating system are you using? From the "appdata" I can guess Windows but I don't like to make assumptions.
I recommend removing this one:
https://github.com/esp8266/Arduino/releases/download/2.7.4/package_esp8266com_index.json
There is no need for that. All the releases are in the other one.