Upgrade to 1.0.270.16 x64 fails with "The installer couldn't create a temporary directory."
Trying to upgrade to 1.0.270.16 fails with "The installer couldn't create a temporary directory. Please check for free disk space and permission to install software." both when using Vivaldi's auto upgrade, and when I tried downloading the installer from the blog - I had to right-click the installer and choose "Run as Administrator" to get it to upgrade. I'm running Windows 10 x64.
I had the same problem and solved it with more permissions on the Vivaldi install folder.
In my case my user had only reading permissions on the folder "C:\Program Files\Vivaldi".
I changed it to full on my user and on the trusted installer.
After that the auto updater worked like a charm.
Setting such permissions opens a security hole - the installer should elevate.
Elevating the installer by "run as administrator" worked for me (with Beta).