Try to deactivate/activate back User Role Editor Pro plugin. If you don’t see URE Pro in the plugin list, rename its folder, e.g. user-role-editor-pro-0, open plugins page – WordPress will deactivate URE Pro automatically. Then rename folder to original back and activate URE Pro. URE grants full list of capabilities to administrator role on activation.
We ran into this issue recently. We use the Menu Editor Pro plugin (Version 2.16.1). When we look into this issue, access to the URE menu item was deselected in the Admin and “current user” profiles. Once we selected them to be displayed/allow access in Menu Editor Pro, the access warning went away and we could get to the settings page for URE.