I use Thunderbird Mobile on a micro SD Card - which is convenient for me to use on my mini mac and a Windows laptop when travelling. On three occasions now my Parallels/Windows 7 has frozen (T'bird non-responsive), So I have to restart Windows in Parallels. When I try to re-open the T'bird, micro-SD - I get a pop up telling me "You need to format the disc in Drive E: before you can use it." It seems that this is because the micro card is seen as not being removed correctly. But this does not seem to happen when a similar occurrence has happened on my Laptop.
Even worse now, I've correctly used 'safely remove..." and when reinstalled the card 'I get The file or directory is corrupted and unreadable'! On both my macmini and my W7 laptop!