If you're getting, the following error when clicking on efinstaller.exe, "file wasn't available on site" it might be the installed anti-virus program, Bitdefender, blocking the download of the latest JC Update. Please follow the instructions to temporarily pause protection on Bitdefender.
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Temporarily Disabling Bitdefender

Try this technique to temporarily disable Bitdefender:

https://www.bitdefender.com/consumer/support/answer/28557/

Then, download and run the latest JC update.

Re-enable Bitdefender protection after installing the latest JC Update.

LogMeIn powered by Bitdefender

Bitdefender powers LogMeIn’s AV security. You can use these steps to temporarily suspend the AV: https://support.logmeininc.com/central/help/suspending-logmein-antivirus-temporarily. If you have an IT person managing AV for your office, they may need to perform these steps for you.

Temporarily suspending your AV should allow you to download and run the latest JC update.