We have DNN 4.5.5 install with a dozen portals. Today for no apparent reason 3 of them (all totally unrelated) started errorring out with:

An error has occurred.
DotNetNuke.Services.Exceptions.PageLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at DotNetNuke.Framework.DefaultPage.Page_Init(Object sender, EventArgs e) at System.Web.UI.Control.OnInit(EventArgs e) at System.Web.UI.Page.OnInit(EventArgs e) at DotNetNuke.Framework.PageBase.OnInit(EventArgs e) at System.Web.UI.Control.InitRecursive(Control namingContainer) at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---

Via the database, I've tried changing skins. I've tried directly accessing different pages via &"tabid=" on the url, including admin pages  such as site Site Settings.

This is on a shared hosted server, so I am wondering if a windows patch could have caused this? I thought it might be skin-related since most of the portals still work fine, but changing the skin has no effect. It can't think of any modules that are the same across all three on all the pages tested.

The RawURL is /Default.aspx?tabid=494&error=Object+reference+not+set+to+an+instance+of+an+object.&content=0

What does "content=0" refer to? These sites share no content other than default dnn content such as terms, dnnmenu, etc., which all the working sites share as well.

Same error info is in the event log, which is to say I have no idea what object reference is not set to an instance of an object.

Thanks for any help or suggestions.