If you get "User ID and password are invalid.try again?" when starting RTC you need to first check that you can login to database in the classic client. Note that the database should be the same as the service tier (the service you are trying to connect with RTC) is connected to.
- Start "classic client with SQL"
- Click File->Database->Open
- Pick the server the database exist one
- Select authentication "Windows Authentication"
- Pick the database
- Press OK
If it works in the classic client make database login synchronization.
- Start "classic client with SQL" and connect to the database as above
- Click Tools->Security->Synchronize all logins
- Answer yes to the question if you would like to synchronize
If it doesn't to connect to the database start SQL server manager and verify that the windows user have permission to login and use the NAV database.