Has anyone found a solution to this issue. We're running 4.8.2 and the issue listed is affecting us. The site is fairly busy (400 users daily, and about 70,000 hits). There is only one portal in this installation. It's not prudent for us to disable caching, which appearntly doesn't help (much.)

Any suggestions?

Method: System.Collections.Generic.Dictionary`2.Insert
StackTrace:
Message: System.Exception: Unhandled Error: ---> System.NullReferenceException: Object reference not set to an instance of an object. at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add) at DotNetNuke.Entities.Modules.ModuleController.GetModuleByDefinition(Int32 PortalId, String FriendlyName) at DotNetNuke.Entities.Portals.PortalSettings.GetSiteSetting(Int32 PortalId, String SettingName) at DotNetNuke.HttpModules.UrlRewriteModule.OnBeginRequest(Object s, EventArgs e) at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) --- End of inner exception stack trace ---

This may fly in the face of every thing holly but I am trying out a theory.. I am turning off Application Pool Recycling.  The reason is, I see problems tend to happen after a recycle. 

I will report back any updates.