The problem is the following two lines of code

            Dim formsNav As XPathNavigator = configNav.SelectSingleNode("configuration/system.web/authentication/forms")

and later

                PersistentCookieTimeout = XmlUtils.GetAttributeValueAsInteger(formsNav, "timeout", 30)
 

If the first line retruns null the second line will fail as described.

So - you need to check if there are any capitalization differences in the path to the forms node.

Charles,

You had it absolutely correct on both where it was coming from, and what the problem seemed to be.  I had my troubleshooting steps down to where you were Charles, but didn't know how to go further.  I had a location tag in my web.config.  In my old hosting setup, GoDaddy, DNN was on the root of the setup.  I had multiple ASP .NET applications below that and I needed to set the inherit attribute to false to prevent the web.config attributes from being inherited.  That was working fine and hadn't been a problem till I upgraded.  I upgraded from version 4.9.1 to 5.0.0 and will be upgrading to 5.0.1 now that this problem has been fixed.  Luckily, as well, I changed hosts so I no longer need to worrry about the inherit attribute.  As soon as I removed it, the problem stopped. 

Thanks for the help.