Errors when trying to install adaptive theme on D8 from backend GUI method When I try to install the Adaptive Theme for Drupal 8 on https://simplytest.me/, I get the following error on /core/autorize.php.


  drupal 8.2.0-rc1
    Update manager
    Error message
    Installation failed! See the log below for more information.  
  
  adaptivetheme
  
  Error installing/updating
      File Transfer failed, reason: Cannot copy /home/r1rkn/www/tmp/update-extraction-3b2e9e06/adaptivetheme/Gemfile.lock to /home/r1rkn/www/themes/adaptivetheme/Gemfile.lock.


This is for the latest Drupal 8 development snapshot version.

How can I fix this error?
First thing is you don't install it. 

All you have to do is make sure adaptivetheme is somewhere in the /themes/ directory.

Then download and install the AT Tools module and it's AT Theme Generator sub-module, then create a sub-theme via the UI (a tab in the Appearance section). The at_core base theme will install automatically when you enable your sub-theme.

Also, this theme will never show up on the Appearance page, it's hidden deliberately, because it's just a collection of scripts and libraries that support features in sub-themes. It's never intended to be interacted with via a UI, or be set as default etc.