Tools > Internet Settings > Tab: Security > Local Intranet > Click: Sites > Click: Advanced
Here you add the URL of the Accesspoint server (e.g.: http://qlikview.domain.com). This should eliminate the need for your user name. By the way, the username you are asked for are the one of the Windows server your QlikView server is running on.
Try to use IIS as webserver, if the problem persist there's some authentication problem: 1) your client is not able to reach your domain controller 2) QVS is not able to verify your credential on the domain controller 3) take a newtork trace and check where authentication stop to work