APM for webserver with basic auth and AD

hi out there I have spend some days now in getting a VS up and run in a testlab where it does a authentication against a AD - but I cannot get it right. I am running a VE 11.3 with LTM & APM behind which I have a Windows 2k8 DC in a domain "testdom.dk" - NTLM domain TESTDOM - and a webserver (win2k8r2 wit IIS7) in that domain which publish a default website. I have changed the authentication on that website from anonymous to basic. When I browse to the site the logon page is presented and I enter my credentials - afterwards the website pops up a logon screen also which tells me that I didn't succeed in getting this right defined since it isn't intercepted by the SSO. Is it my authentication level on the webserver wich could be wrong? best regards /ti