This usually indicates a corrupted install. Try these steps: # do NOT uninstall, as that may delete your message folders # locate the program, either at c:\program files or c:\program files (x86) and delete it # download and install your preferred version. I recommend ver 128, but it's your call. # if you receive a compatibility error, locate the profile and delete a file named compatibility.ini (profile will be at c:\users\<yourid>\appdata\roaming\thunderbird\profiless