My computer suddenly started the above error message for multiple programs. The local computer shop was able to sort out what appeared to be the root cause and that recovered some things but I still needed to reinstall a number of programs. The program I am terrified of reinstalling is Thunderbird. All my emails on five email accounts since 2011 are stored in TB and I naturally do not want to lose any of them. The major problems are the computer is running Win7 Enterprise and I am 82 years old so I am prone to needing things spelt out in greater detail than many others. Can anyone provide a way to reset the program permissions (preferable) or identify the best way to reinstall and still access all my historic emails? Thank you