Error Message looks something like this:
Fatal error: Cannot redeclare wphr_fs() (previously declared in /home/xxxxxxx.com/public_html/wp-content/plugins/wp-hr-manager/wp-hr-manager.php:46) in /home/xxxxxxx.com/public_html/wp-content/plugins/wp-hr-manager-premium/wp-hr-manager.php on line 75
Cause: Free version is active alongside Pro version
Solution: Deactivate free version (you may also need to deactivate WP-HR Manager and then reactivate it)