I didn’t have an activation error. Installation and activation worked.
However, when I checked the ‘Enable Debugging’ control in the Airpress admin page, the Airpress plugin code wants to log stuff in the airpress.log file. This file is not created during installation.
To fix, you will need to create the text file, from the command line or a file manager. On your Mac or linux host shell, go to your WordPress document root directory, and do this:
sudo touch wp-content/plugins/airpress/airpress.log
Set the permissions too. Assuming the group is the http server:
sudo chown 664 wp-content/plugins/airpress/airpress.log
On Windows, try something like this. You just need to create the file.
echo hey > wp-content\plugins\airpress\airpress.log