For any poor souls who are struggling with this issue, this is what worked for me...
I am running this locally. That is the key! In my code, there were 2 cookies created before the .Redirect method call: The code looked like this:
Dim C As HttpCookie
C = FormsAuthentication.GetAuthCookie(custID.ToString, False)
C.Domain = "ourdomain.com"
Response.AppendCookie(C)
Dim C2 As System.Web.HttpCookie = New System.Web.HttpCookie("ProfileUsername", P.UserName)
C2.Domain = "ourdomain.com"
Response.AppendCookie(C2)
I needed to change the .Domain to ".localhost". It MUST have at least one dot in the name.
Also, in the web.config file, in the element authentication. The 'mode' is 'Forms'. An attribute of 'Forms' is domain=".localhost"
That got my test to accept my test member and move on to the part of the code that I needed to test.