Also to add to Kens post
You might need to make sure that none of the pages are cached. If you're
using a master page, you can put the following code at the beginning of
Page_Load
Response.Expires = 60
Response.Expiresabsolute = Now() - 1
Response.AddHeader("pragma","no-cache")
Response.AddHeader("cache-control","private")
Response.CacheControl = "no-cache"
Hope that helps
Patrick