The reason why you get the above message when launching SteelCentral Portal 2.0 platform app from web app when you are logged in as local admin user created is because the local admin user does not exist in the Platform web app. These are 2 independent appliactions and we need the local admin user created in both applications.
Once you login as admin into the Platform web app you can see that the user mentioned in the above example (portaluser) does not exist in Platform web app user list
You will have to create the same local user in Platform web app for you to launch Platform web app from Portal web app.