Thunderbird 78.1.1 Switching from W7 to W10. W7 configuration: profile is on separate HD - not C:\. Clean install of W10 on new HD and I had to enter all my email accounts and somehow somehow managed to get tbird to link to existing profile on separate HD so addresses & rules, are 'there'. W10 version working fine. Thunderbird is about the only thing that works satisfactorily in W10 so I went to dual boot to spend most of my time in W7. On restoring previous W7 OS image [on a separate HD from W10 OS], tbird now demands that I not use old profile w new tbird version. That's the best way I can interpret the message. I'm guessing the OS/image version that says this [from June, '20] doesn't like the profile version that was doing just fine before I started this switch in mid July. So I've started over and re-entered all the email addresses [as I did on W10 connfiguration] but I've tried 3-4-5 ways to trick Thunderbird into using the old profile which is still the same file on the same separate HD that the W10 Thunderbird is using and I just can't get that to happen. I exported/imported address books [from W10 to W7] but didn't get the filters. I don't know what else I am missing, but I think all I need is teh dozens of filters I've set up over the years. IT looks like current W7 version of tbird is working fine except no filters. I see all the same sent/received emails when running tbird from either OS. How can I get the filters back into W7 Thunderbird? Can/Must I have tbird running or not running? Can/Must I drive things from W10 tbird active and W7 is just anothere data HD? Or drive from W7 tbird active and W10 is just another data disk? Simplest could be just connect current W7 tbird to same old profile on separate HD. If this is not part of the process, then I will have to do it later anyway but that should be an easier process. Several utubes etc on how to do that. I do not have enough room on C:\ OS HD for email data. That's why the profile is on separate HD. My goal is to have both W7 & W10 tbirds using the same profile - of course, only one such alive at a time. When one Tbird updates, boot to the other OS and update that tbird. If this absolutely cannot be done, please tell me so. Many thanks in advance!!