Simple forms authenticated website does not redirect after login

I have a website built on a simple authentication model.
It runs fine locally and on local IIS, but it is not redirecting to the default page after typing in the correct credentials, all this in the test server.

The code goes as follows:

//Web.config

<compilation targetFramework="4.0" /> <httpRuntime maxRequestLength="50000" /><customErrors mode="On" defaultRedirect="exc/exc.aspx?e=1"><error statusCode="404" redirect="exc/404.aspx?e=404"/></customErrors> <authentication mode="Forms"><forms loginUrl="admin/login.aspx" defaultUrl="admin/main.aspx" /></authentication> <authorization> <allow users="*" /></authorization> </system.web><location path="admin"><system.web><authorization><deny users="?"/></authorization></system.web></location><location path="admin/css/cms.css"><system.web> <authorization><allow users="?"/></authorization></system.web></location><location path="admin/css/styles.css"><system.web><authorization><allow users="?"/></authorization></system.web></location><location path="admin/images"><system.web><authorization><allow users="?"/></authorization></system.web></location><location path="exc/exc.aspx"><system.web> <authorization><allow users="?"/></authorization></system.web></location>

//login.aspx
//The form action property is blank and AutoEventWireup is true.

//login.aspx.cs

protected void btnAuth_Click1(object sender, EventArgs e)

{

//Some code not shown...

//User Validation

ValidateUserResponse response = new ValidateUserResponse();
response = service.ValidateUser(request);

if (response.State == true)
{
FormsAuthentication.RedirectFromLoginPage(request.Alias, False);
}

}

//SignOut

protected void Page_Load(object sender, EventArgs e)
{
FormsAuthentication.SignOut();
Response.Redirect(FormsAuthentication.LoginUrl);
}

On the test server the URL looks something like this:

http://192.168.1.58/TestSite/admin/login.aspx

On VS2010 works well as well on my local IIS once published, but don't understand why isn't redirecting to the default page
after the login when published on the TestServer. Showing that the website requires to log in and a 403 forbidden error.

Locally I have tested it with both URL forms and works (the virtual folder name is different):

http://192.168.1.58/TestSite1/admin/login.aspx 
http://localhost/TestSite1/admin/login.aspx 

I'd appreciate any suggestions on the matter to make it work.

Thank you.