My guess is you made the copy while Thunderbird was running. That never seems to work because Thunderbird still has access to the files. I suggest you repeat the copy. Also, since you're copying from the appdata\roaming folder (which includes the Thunderbird folder), be sure to install Thunderbird on new pc first.

David, thanks! That is NOT the case. I do know enough to close Thunderbird and, even so, I did read the details on moving Thunderbird. This is something else. (and I have tried this at least half a dozen times with the same results.)

This is a hardware problem, not a Thunderbird problem. I did a quick web search for error 0x800701b1 and there are many web sites with info. The key here is that the error message is stating the device doesn't exist.

David, yeah, isn't that the truth. Why is it looking for another device? What in the Thunderbird profile is saying it needs to go to another device? The device is working fine for EVERYTHING else, it's just the Thunderbird profile that won't copy to it? It makes absolutely NO sense! (Don't get me wrong, I appreciate your answer, but something in the profile is telling File Explorer to copy to some device that is not there... It's REALLY frustrating as I've been messing with this for a week!)

But all of that is done by Windows. I suggest just browsing the USB and viewing some of the files and maybe copying some files individually. The profile is just a windows folder.

David, Well, I typed a reply to you, but managed to lose that! So, here goes again! Pulling my head out of the nether regions of my body and my foot out of my mouth... You are absolutely correct that it is a SOURCE drive problem and not a DESTINATION drive problem! Sometimes even an old guy with eyesight problems makes mistakes, even though he's been working with computers since 1963! I really should know better. Thanks for your patience and good nature and not out-and-out calling me a dummy! I haven't completely solved the problem, but you've at least got me looking in the right place! Thanks, again!

Funny. No, there are no dummys here. And I've been with computers since 1964, so our hair is probably the same white color.

David, Got ya'! I didn't know there were still any of us old guys around here! I've done tech support work before and also was a SysOp with Novell for some years, so I've done my share of responding to questions. I really do appreciate your good nature and patience. Please have a great day!

Don