You may have downloaded and tried to open the new version of Firefox or Thunderbird. Each time, you try to open, you get the 7-zip unspecified error. Here is the way to fix it.
You have uninstalled, reinstalled and restarted your pc, still no luck. What do you need to do?
It is is usually a result of a corrupted download. Delete the installers you have and download fresh ones. Then clean your Operating system’s temporary folder and then Install again. It should work rightly now.