My wife and myself recently changed our 2 computers. On both we are separate users and administrators. Both use Thunderbird, and each has his own IMAP e-mail account. Mr. "A" has "axyz@yahoo.it"; Mrs "B" has "bxyz@yahoo.it" With our old computers both e-mail accounts worked flawlessly. We then changed one computer, which run the beta version of Windows 10. Account "axyz" under user "A" was set up without problems. Account "bxyz@yahoo.it" under user "B" could not be set up, getting the above mentioned error message. We upgraded to the final version of Windows 10, and also the account "bxyz" could be set up without problems. Then we changed the second computer, and upgraded from the preinstalled Windows 8 to Windows 10. Account "bxyz" was set up without problems under user "B". This time account "axyz" under user A could not be set up, getting the same error message. At this point I decided to try to set up the "axyz" account as an additional account under user B, and it worked without problem. However, I am still unable to create "axyz" account under "A" user. What's going on ????? Thanks Aldo Cecchini