After upgrading to Episerver 11 from an earlier version you get an "Object reference not set to an instance of an object" error in the initialization step or you get a "ReadConfig()" error during the database migration.

This is caused by a breaking change in Episerver 11.0.0 where some objects where moved from the base EPiServer.Framework module to the EPiServer.Framework.aspnet module. To fix this go into your web.config file and look for:

<add virtualPath="~/cms/" physicalPath="modules\_protected" name="ProtectedAddons" type="EPiServer.Web.Hosting.VirtualPathNonUnifiedProvider, EPiServer.Framework"/>

And update it to read:

<add virtualPath="~/cms/" physicalPath="modules\_protected" name="ProtectedAddons" type="EPiServer.Web.Hosting.VirtualPathNonUnifiedProvider, EPiServer.Framework.aspnet"/>