Forms auth. don't work going from NET 1.0 to 1.1

[Arne Håveland]

I have a web system with forms authenticationthat works
good.
When I uppgraded from .NET 1.0 to 1.1 I can't leave the
login page.
If I change to
Server.Transfer("UserManager.aspx")
it works, but if I use
FormsAuthentication.SetAuthCookie("UserManager.aspx",
True)
Response.Redirect("UserManager.aspx", True)
it won't work in ver 1.1 but still do in ver 1.0
/Arne