Looking for help regarding a recent updgrade to Umbraco 6.0.

Website loads correctly and back-office (Admin Area)  looks as it did in the previous 4.9 version.    Following the general installation and specific installation instructions from here http://umbraco.codeplex.com/releases/view/101178.  

So basically we went from 4.9 to 4.10 to 6.0 in our upgrade process.  At 4.10 we ran the fixup package before going to 6.0.

Even though everything looks correct, when we attempt to save or even publish a current or new page we get an error message (attached).  I have pasted below as well:

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Object reference not set to an instance of an object. 

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error: 

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace: 

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

   Umbraco.Core.Models.ContentBase.SetValueOnProperty(String propertyTypeAlias, Object value) +189

   Umbraco.Core.Models.ContentBase.SetPropertyValue(String propertyTypeAlias, String value) +9

   CallSite.Target(Closure , CallSite , Object , String , Object ) +169

   System.Dynamic.UpdateDelegates.UpdateAndExecuteVoid3(CallSite site, T0 arg0, T1 arg1, T2 arg2) +468

   Umbraco.Core.Models.ContentBase.SetValue(String propertyTypeAlias, Object value) +243

   umbraco.cms.businesslogic.web.Document.Save() +178

   umbraco.cms.presentation.editContent.Save(Object sender, EventArgs e) +2154

   System.EventHandler.Invoke(Object sender, EventArgs e) +0

   umbraco.controls.ContentControl.saveClick(Object Sender, ImageClickEventArgs e) +337

   System.Web.UI.WebControls.ImageButton.OnClick(ImageClickEventArgs e) +115

   System.Web.UI.WebControls.ImageButton.RaisePostBackEvent(String eventArgument) +124

   System.Web.UI.WebControls.ImageButton.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10

   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13

   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +35

   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1724

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Has anyone else ran across this issue?  This entire upgrade process has been painful.  We have used application such as winmerge to go through and check all changes even before merging.  We feel as though we have thoroughly read through and performed all actions necessary for the upgrade. 

Any insight would be greatly appreciated.  Thanks JR.