The error was with the Thunderbird program itself, it sounds like it tried to update and something went wrong. You would have needed to uninstall the program. Did you uninstall the Thunderbird program ? It was originally put into the 'Program Files (x86)' folder because originally you installed and used a win32 version of Thunderbird. If you had later changed to use win64, it should have installed in the same 'Program Files (x86)' folder because Thunderbird developers found a potential issue with locating the original profile if it was put into the expected 'Program Files' used for win64 programs. You would also have needed to install the same version as previously used - which might not be the current release and install it in Program Files (x86) folder. So, it would seem when Thunderbird started it could not locate the original profile and so a new profile was created. You then created a new mail account in the new profile. The old profile is not corrupted, it is just not being used. Currently what type of account are you using in Thunderbird is it POP or IMAP ? If IMAP then you would have to import those emails into the 'Local Folders' mail account. Previously, what type of account are you talking about? Was it a Pop mail account ? Or are your talking about mail stored in the 'Local Folders' mail account ? Or both ? Also post an image of what you see in the 'Profiles' folder this location: C:Users/ User Name/Appdata/Roaming/Thunderbird/'''Profiles''' folder Tell me which profile name you are currently using