Steinberg Download Assistant: Content installation causes error message on macOS

The installation of content on macOS fails. An error message appears. 

...*.vstsound could not be opened.

This problem seems to occur only when the target volume is an external disk connected to a computer running macOS. 

Please follow these steps: 

• Open the download folder defined in the Steinberg Download Assistant.
  The default location is: /Users/Your Username/Downloads/Steinberg/OSX/
• Inside the OSX folder, open the folder that belongs to the content you've tried to install.  
• Copy the downloaded vstsound file to the desired location on the external hard drive. 
• Repeat this for other vstsound files you want to install on the external hard drive. 
• Once all files have been copied completely, double-click one of the vstsound files. 
• The Steinberg Library Manager opens. 
• Enable the option "Register in Place". This means, the file(s) will not be moved, but registered.

• Click OK to finish the installation.
• The Steinberg Library Manager confirms the installation by prompting "VST Sounds registered successfully". 

This installation issue is currently investigated and will be fixed as soon as possible.