Version 128 is the ESR version that is updated once a year, while 137 is the new 'release' version updated at least monthly, like Firefox. You can update 128 to 137 by manually downloading the 137 installer from thunderbird.net, at least with Windows. The newer version should read the existing profile without issue. On Linux, updating is usually done through the distro's update mechanism. I don't think there's any great advantage to having both on 137, and there might be some advantages as 128 is possibly more stable. As to why the laptop with 137 won't download, I can think of an example such as AT&T accounts that require a different secure mail key for each computer, even for the same account. It might help if you post any error messages.