Common problem:

I try to install de "Public Institution Theme" but when I try to activate "PE Public Institutions Plugin"  show me these errors:
Fatal error: Can't use function return value in write context in /var/www/html/wp-content/plugins/pe-public-institutions-plugin/pe-public-institutions-plugin.php on line 152

I've installed and activated the PE School theme, and have installed the required PE School Plugin, but am unable to activate it. The error message I'm getting is:
Fatal error: Can't use function return value in write context in .../wp-content/plugins/pe-school-plugin/pe-school-plugin.php on line 154

Solution:

The problem is related to very old PHP version on your server. 
It seems you are using very old PHP version < 5.6.
We recommend updating PHP on your server at last to 5.6 or even better to 7.x version for security and performance reasons.