dont forget the templates

Step 15 read all entries form modules, languages and templates to reload the "latest" infos to the addon-table in the database
for this job, the upgrade-script open the folders languages, modules and templates and read from there the content
in the language-folder, it reads only the PHP-Files like EN.php, ES.php etc
in the other folders, it read the file info.php
the error-message talk about the function get_variable_conten
t()
this function reads the entries from this files and take from there only the content
for example: from this definition
$module_description = 'This page type is designed for making a news page.';
the function use only the text "This page type is designed for making a news page." and write this into the addon-table
the error-message means, some of this definitions are empty or not avaiable, is it not a string
be sure, that you have no ZIP-Files in the folders "languages, modules and templates", because, the script try to unzip this zip-files also
check also your temp-Folder and delete there possible Zip's. Maybe, its a good solution, if you clear the wb-own temp-folder and delete possible files from there