As a temporary fix I have done this:
1 – Added licence key to wp_config, But using this code:
Your readme.txt file says to use
I think that is the wrong constant.
2 – I completely removed (commented) the function is_license_key_editable() in plugins/user-role-editor-pro/includes/pro/class-ure-lib-pro.php
By doing this I was able to activate the plugin again.