I was saving a content page, when I suddenly got a web config error.  the error details are below.

I have checked the database and I am struggling to identify any null value.  The problem I have now have is that every page is getting this error.

Thanks

Andy

[NullReferenceException: Object reference not set to an instance of an object.]

   umbraco.cms.businesslogic.ContentType.<InitializeVirtualTabs>b__11(TabI a, TabI b) +16

   System.Collections.Generic.ArraySortHelper`1.QuickSort(T[] keys, Int32 left, Int32 right, IComparer`1 comparer) +178

   System.Collections.Generic.ArraySortHelper`1.Sort(T[] keys, Int32 index, Int32 length, IComparer`1 comparer) +204

[InvalidOperationException: Failed to compare two elements in the array.]

   System.Collections.Generic.ArraySortHelper`1.Sort(T[] keys, Int32 index, Int32 length, IComparer`1 comparer) +12688022

   System.Collections.Generic.List`1.Sort(Comparison`1 comparison) +166

   umbraco.cms.businesslogic.ContentType.InitializeVirtualTabs() +765

   umbraco.controls.ContentControl..ctor(Content c, publishModes CanPublish, String Id) +724

   umbraco.cms.presentation.editContent.OnInit(EventArgs e) +603

   System.Web.UI.Control.InitRecursive(Control namingContainer) +133

   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1970