Just tried upgrading from 4.7.0 to 4.8.3 following the guidelines put out by Mitchell Sellers.  After running the install.aspx, I try to start the site but get the following error:

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.GetPortalSettings(Int32 TabId, PortalAliasInfo objPortalAliasInfo) +91
   DotNetNuke.Entities.Portals.PortalSettings..ctor(Int32 tabId, PortalAliasInfo objPortalAliasInfo) +83
   DotNetNuke.HttpModules.UrlRewriteModule.OnBeginRequest(Object s, EventArgs e) +3303
   System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +92
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +64

Any suggestions?

Me three.  I'm just upgrading from 4.05.05 to 4.8.4 and the upgrade meets with success until the last stage and then gives this same error  -  verbatim - when I boot to the site afterwards.  Please somebody help if you can!

Kevin wrote I'm here with the same problem. Foudn this thread by searching, and it appears that any thread involving this subject has 0 replies.  Its as if nobody  knows how to solve it. :\ i install, run through configuration, then, when installation is complete, click the "Go to homepage" button, and this is when i receive this error.   Help!?!?   Kevin    smithd wrote   Just tried upgrading from 4.7.0 to 4.8.3 following the guidelines put out by Mitchell Sellers.  After running the install.aspx, I try to start the site but get the following error: 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.GetPortalSettings(Int32 TabId, PortalAliasInfo objPortalAliasInfo) +91    DotNetNuke.Entities.Portals.PortalSettings..ctor(Int32 tabId, PortalAliasInfo objPortalAliasInfo) +83    DotNetNuke.HttpModules.UrlRewriteModule.OnBeginRequest(Object s, EventArgs e) +3303    System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +92    System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +64   Any suggestions?

Sad... a month and some change later and i'm posting the same issue with no replies to fixes/suggstions?

mine is on a fresh install... install process successful at all points, loading the finished site brings the errors: mine are slighly different...
 

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.HttpModules.UrlRewriteModule.RewriteUrl(HttpApplication app) +378 DotNetNuke.HttpModules.UrlRewriteModule.OnBeginRequest(Object s, EventArgs e) +1180 System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +92 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +64