download and install fiddler and look at the requests, it's likely that one is causing the cookie to expire - typically either a redirect to another aspx page (e.g. a 404) or else a request to a .net file (such as aspx) that doesn't contain portalid or tabid (DotNetNuke cannot tell what portal requested it so treats it as a request for a new portal and logs the user out)

---

Buy the new Professional DNN7: Open Source .NET CMS Platform book Amazon US

Once fiddler is open , if a trace begins running, you'll want to uncheck "File -> Capture traffic" or press F12. Clear the entries by using "Edit -> Remove -> All Sessions". Now browse to the area of the site causing issues, and then press F12 to start a trace, visit the exact problem location, and then press F12 to finish. You can now inspect the session details and use it to follow the exact sequence of page requests (including any "invisible" response.redirects or server.transfers) as well as spot common errors such as :

Missing files (shows as 404 errors)
lost authentication (click on a page name, and then click inspectors in the right tab and examine if all cookies are passed as expected)
access denied errors (showing up as 401 errors - the sub number indicates the exact failure e.g. 401.3 is an "access denied by ACL on resource" error. This means that you have not granted sufficent permissions to access that file.

---

Buy the new Professional DNN7: Open Source .NET CMS Platform book Amazon US