I already installed DNN on my root (http://localhost) on one Sql Server database (dbMain) with objecQualifier="MainPortal"

Next, i want to install another DNN site under the root (e.g: http://localhost/mysite) with the same database but different on objecQualifier. I use "MySite" as objectQualifier. I don't want to make "mysite" as child portal (using Host --> Portals menu), but fresh DNN installation.

I use the same step-by-step installation like i did for http://localhost. It works, but after i 'Click here to access your portal', i have some strange behavior. I do it twice like this :

1. I change web.config (for http://localhost/mysite) like this :
    objectQualifier="MySite"

    When i do like that, an error "object reference not set to an object" occured. So i try to reinstalling with configuration like this :
    objectQualifier="MySite"
    .... applicationName="MySite"

    When i do like that, installing successfully. But i have another error like this in the URL 'http://localhost/mysite/Home/tabid/0/ctl/Login/portalid/0/Default.aspx?returnurl=%2fmysite%2fDefault.aspx' 
    No Home menu, can't access Login page and Register page. Installation just show mainpage with no action at all. I don't know what's wrong.

Can somebody give me a clue how to install one DNN v4.3.1 on root and then add new fresh DNN installation as virtual directory.

Thank you very much.