I can’t seem to be able to give Admin rights to the above plugin – they have both Editor and Shop Manager rights assigned to their membership and have been allocated rights to the plugin but it doesn’t allow them to use as an admin
Ultimate Auction Pro plugin uses directly ‘administrator’ role to protect all its menu items. Moreover it intensively checks if user has the ‘administrator’ role through its code.
This means that is no chance to replace ‘administrator’ to some other role without headache after every plugin update.
Contact plugin developer. It’s quite better to use user capabilities (or custom role) to protect the plugin, in order a client may decide himself to whom allow to use this plugin.
It’s possible with WordPress multisite where you may revoke some capabilities from single site ‘administrator’ role.
You may fake ‘Ultimate Auction Pro’ plugin by adding a user capability with ‘administrator’ ID to the user role. But be ready that such user will get access to any other plugin which similar uses ‘administrator’ role to protect access to its functionality.