I have been trying to help a client using Thunderbird who began getting 'Thunderbird is running' errors when starting it. This has been going on for a number of months. I have tried the delete parent.lock file, starting in safe mode, reinstalling, rebuilding mail data (has one gmail account imaped in it) but when I think it is fixed and leave her it happens again. She only has one computer so I don't believe it could be from having two instances using the profile. She thinks it started after a Windows 10 upgrade months back. Side note, I was giving up and installed Office 365 for Outlook and the trial version wouldn't load her Gmail imap account (it is near 15 gigs of mail) I am open to any suggestions as I clearly can't fix this myself.