Hi.  One of our sites stopped functioning normally.  If you try to access it by going to www.mysite.com, you get the following error:

Server Error in '/' Application.
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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.]
   DotNetNuke.Entities.Portals.PortalSettings.VerifyPortalTab(Int32 PortalId, Int32 TabId) +320
   DotNetNuke.Entities.Portals.PortalSettings.GetPortalSettings(Int32 TabId, PortalAliasInfo objPortalAliasInfo) +2413
   DotNetNuke.Entities.Portals.PortalSettings..ctor(Int32 tabId, PortalAliasInfo objPortalAliasInfo) +83
   DotNetNuke.HttpModules.UrlRewriteModule.OnBeginRequest(Object s, EventArgs e) +2677
   System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +92
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +64

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Version Information: Microsoft .NET Framework Version:2.0.50727.1433; ASP.NET Version:2.0.50727.1433

Here's some information about the site:

• DNN 04.05.01
• Windows Server 2000 Standard, SP4, Latest Patches
• SQL Server 2000 Standard

It's a simple site.

• No 3rd party skins.
• No 3rd party modules.
• It's the only portal in this instance of DNN.

The interesting thing is that I can login if I'm specific with my URL.  For example, if I type (http://www.mysite.com/dotnetnuke/Home/tabid/36/Default.aspx), I can login successfully as host.

The Event Viewer shows several similar error messages like:

AssemblyVersion: 04.05.01
PortalID: -1
PortalName:
UserID: -1
UserName:
ActiveTabID: -1
ActiveTabName:
RawURL: /ScriptResource.axd?d=h5veskUv3v7v5Hfn50dP5T-gtllc21tuxARuABfFjLlcRpEMHegtUTXwtbRcxaR50&t=633049125920000000
AbsoluteURL: /ScriptResource.axd
AbsoluteURLReferrer: http://www.mysite.com/Admin/SiteSettings/tabid/40/Default.aspx
UserAgent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 2.0.50727)
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 29e6fe28-ba36-4ad6-9c14-a89554483405
InnerException: Unhandled Error:
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: DotNetNuke.Entities.Portals.PortalSettings.VerifyPortalTab
StackTrace:
Message: System.Exception: Unhandled Error: ---> System.NullReferenceException: Object reference not set to an instance of an object. at DotNetNuke.Entities.Portals.PortalSettings.VerifyPortalTab(Int32 PortalId, Int32 TabId) at DotNetNuke.Entities.Portals.PortalSettings.GetPortalSettings(Int32 TabId, PortalAliasInfo objPortalAliasInfo) at DotNetNuke.Entities.Portals.PortalSettings..ctor(Int32 tabId, PortalAliasInfo objPortalAliasInfo) 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 ---
Source:
Server Name: IIS

The site was fine a week or two ago.  Then it sat there unused for several days.  Then when we went to access it, we discovered the errors above.

But wait...there's more!  If I try to make changes to page settings, or add a new page, I get this error in my browser:

Error
A Runtime Error has occurred.
Do you wish to Debug?
Line: 0
Error: “Webform_PostBackOptions’ is undefined”

Here's the offending line of code:
Webform_DoPostBackWithOptions(new Webform_PostBackOptions("dnn$ctr370$ModuleSettings$cmdUpdate", "", true, "", "", false, true))

I've got over 8 hours into the problem.  I've scraped Google and Live extensively.  Lots of people have similar errors.  However, whenever anyone has my exact error, there's never been a follow up with a solution.

The PortalAlias table contains a single record:

• PortalAliasID: 1
• PortalID: 0
• HTTPAlias: www.mysite.com

Here are some other settings:

Admin -> Site Settings:
     Advanced -> Page Management
          Splash Page:  <None Specified>
          Home Page:  <None Specified>
          Login Page:  <None Specified>
          User Page:  <None Specified>
          Home Directory:  Portals/0
Host -> Host Settings
     Advanced -> Performance Settings
          Page State Persistence:  Page
          Module Caching Method: Disk
          Performance Setting: Moderate Caching
          Authenticated Cacheability: ServerAndNoCache
          Compression Setting: No Compression
          Use Whitespace Filter: No

Things that I've tried:

• Add a second PortalAlias
• disable Compression in Web.Config
• Remove "www" from www.mysite.com in PortalAlias
• Add space to the end of Web.Config to clear cache (because I get the silly postback error if I click the "Clear Cache" link.)
• Flushed temp files on several clients to no avail
• Setting the home page so that it defaults to a specific TabID (in Portals table).

I appreciate any and all assistance on this matter.  At this point, I basically have no choice but to go back to a backup.  I would prefer a surgical solution, if possible, though.

Also, if anyone thinks that it would behoove me to upgrade this site to DNN 4.8.4, I'll do it.  I was going to do that anyway, before we discovered the errors.  I've just been nervous to attempt an upgrade while the existing site is malfunctioning so dramatically.

Thanks!
Van