I’ve reviewed the code of the plugin you’re using.
As you might be aware, the plugin hasn’t been updated in 6 years. Unfortunately, some of variables and functions it uses in it’s code don’t even exist anymore. For instance has_cap which it uses to determine who can see the reject/apply buttons was removed in WordPress 2.0.
If you need the functionality of this plugin, I would recommend hiring someone to rewrite it to work on new version, since there’s alot of deprecated code in there thats going to stop working in future WordPress versions.
-Chris