forms authentication brings up dialog

[Maximilian]

I have a very simple site with forms authentication. Everything works
allright when running locally when deploying it on the real server it doesnt.
The thing is I get a dialog prompting me for credentials rather than
redirected me to Login.aspx as it should (and does locally). Why?
And about this cred-dialog. I guess it could be nice to use it sometimes,
but can it be used with custom authentication? I mean can a validate the
input from this dialog in some customized way? or against users specified in
the Web.config file? Or is it only for Windows-authentication?

~/Web.config:

<authentication mode="Forms">
<forms loginUrl="admin/Login.aspx">
<credentials passwordFormat="Clear">
<user name="test" password="test" />
</credentials>
</forms>
</authentication>

~/admin/Web.config:

<system.web>
<authorization>
<deny users="?" />
</authorization>
</system.web>