Forms Authentication - IE problem

 Hi folks,
I already implemented some kind of Forms Authentication. I got the following problem - When I'm using IE(7, 8) ONLY (FF, Opera, Chrome - they are OK) it is impossible to to get logged and get redirect to specified page from the Login.aspx. This problem occurs ONLY with IE. After passing some validations and creating ticket the Login page is reloaded again, and NO redirect to Default page exists. Address bar consists always this string:
      http://localhost:3706/Login.aspx?ReturnUrl=%2fdefault.aspx 
 
In Global.asax - HttpContext.Current.User is ALWAYS NULL under IE.

Here is my code implementation:
Web.config:
<authentication mode="Forms">
   <forms defaultUrl="Default.aspx" loginUrl="Login.aspx" protection="All&qu ...