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Lightning 4.0.1 won't install in Thunderbird 38.1.0

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I had similar issues with 4.0.0.1 and 38.0.1 (https://support.mozilla.org/en-US/questions/1067957)

Thunderbird upgrade to 38.1.0 went fine. After a Thunderbird restart it was fine. After a PC restart, I lost my calendar. Checked add-ons, and Lightning has gone. Tried installing 4.0.1. Same issue as last time, after restart it still says it needs a restart to install. I've tried deleting the extension entirely out of my profile, which fixed my problem in the previous version. But it doesn't make a difference. I've tried installing 4.0.0.1 as well, same problem. Tried installing both via file. No difference. Nothing I do gets Lightning to finish installing. No matter what I do it just continually says it needs a restart to install.

Any help would be greatly appreciated, I rely on my calendar a lot.

I had similar issues with 4.0.0.1 and 38.0.1 (https://support.mozilla.org/en-US/questions/1067957) Thunderbird upgrade to 38.1.0 went fine. After a Thunderbird restart it was fine. After a PC restart, I lost my calendar. Checked add-ons, and Lightning has gone. Tried installing 4.0.1. Same issue as last time, after restart it still says it needs a restart to install. I've tried deleting the extension entirely out of my profile, which fixed my problem in the previous version. But it doesn't make a difference. I've tried installing 4.0.0.1 as well, same problem. Tried installing both via file. No difference. Nothing I do gets Lightning to finish installing. No matter what I do it just continually says it needs a restart to install. Any help would be greatly appreciated, I rely on my calendar a lot.
Attached screenshots

Chosen solution

I think we need to explore why you were unable to update files last time. Personally I am thinking external security software. So to that end I suggest you restart the machine in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 8, Windows 7, Windows Vista, Windows XP, OSX

Once in safe mode see if the install will complete. I think some security product is blocking the update. This could be windows UAC, your anti virus or anther program entirely.

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I've tried deleting the extension entirely out of my profile,

I suppose that means you did delete the Lightning extension folder in the 'extensions' folder of your profile. Do that again when Thunderbird is closed. Also look for a folder 'staged' in the 'extensions' folder. Delete that as well. Then try to install Lightning again. Use the latest version from https://addons.mozilla.org/en-US/thunderbird/addon/lightning/

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Tried all of that already. Even thrown in a computer restart after deleting the folders. No difference.

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Chosen Solution

I think we need to explore why you were unable to update files last time. Personally I am thinking external security software. So to that end I suggest you restart the machine in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 8, Windows 7, Windows Vista, Windows XP, OSX

Once in safe mode see if the install will complete. I think some security product is blocking the update. This could be windows UAC, your anti virus or anther program entirely.

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You were correct. Sage mode allowed me to install the addon no problem. So must be something blocking it on my PC. Next time there's an update I shall try turning some things off and see whats blocking it. But I'm sorted now, thanks!