What is the status of Lightning in the Add-ons Manager? please provide a screenshot with the entry for Lightning visible. https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem

It appears to be enabled, see attached.

Edit: I tried disabling, then enabling again. That did not work either. I've also tried restarting my PC.

If you're still on Thunderbird 38.3.0 update to 38.4.0.

Thunderbird has updated itself to 38.4.0 but still no calendar.

As a temporary solution I've started to use Google calendar. I don't really want to switch, but...

pikestaff, Thank you for reporting this.

1. Immediately after startup, is anything related to calendar seen in tools | error console.

2. Does starting in safe mode, and then starting normally help? (please do #1 first)

https://support.mozilla.org/en-US/kb/safe-mode

Hi Wayne, thank you for responding.

1. Messages in the error console include:

Could not read chrome manifest 'file:///C:/Program%20Files%20(x86)/Mozilla%20Thunderbird/chrome.manifest'. Could not read chrome manifest 'file:///C:/Users/Kevin/AppData/Roaming/Thunderbird/Profiles/aersevaj.default/extensions/%7Be2fda1a4-762b-4020-b5ad-a41df1933103%7D/chrome.manifest'. No chrome package registered for chrome://lightning/locale/lightning.properties No chrome package registered for chrome://lightning/locale/lightning.properties (yes, this appeared twice)

2. Starting in safe mode and then starting normally did not help. I looked at the error console again and got the same messages plus, in addition, two instances of:

No chrome package registered for chrome://calendar/skin/cal-icon32.png

pikestaff, what language version do you have installed?

Matt, I don't know for sure and I don't know where to find this information. However, I'm located in England and the only dictionary installed is English/United Kingdom. So I assume it's British English.

This is what I'd try: Determine your profile folder via Troubleshooting Information.

At the top right of the Thunderbird window, click the menu button , then select Help > Troubleshooting Information > Profile folder > Open Folder.

This will open the profile in Windows Explorer.

Close Thunderbird.

Temporarily stop your anti-virus real-time scanner.

Navigate to the extensions subfolder, and locate a folder {e2fda1a4-762b-4020-b5ad-a41df1933103}. It is the Lightning extension. Delete that folder if it exists.

If there is a 'staged' folder delete it as well.

Start Thunderbird, and install Lightning again. For Thunderbird 38.4.0 the corresponding version of Lightning is 4.0.4.1.

If it did work this time, turn anti-virus back on.

That worked, thank you!

I have the exact same messages/errors in the console as stated above. I have done this 3x now with TB 38.6. This is the 2nd time lightning calendar has just disappeared and the fix last time (found here: https://groups.google.com/forum/#!topic/mozilla.support.calendar/Ds0kNdPDNXY)

did not fix this time around. Since this is a newer version than the original poster's with same issue, is there something else I can try? I use this calendar for business and cannot afford to lose it.

gutterman1223,

please start a new thread for your problem. Provide as many details as possible.

Thanks for responding. I did start a new thread here:

https://support.mozilla.org/en-US/questions/1113939

If you need more info, let me know.