After upgrading from Umbraco 4 to 4.5.2 using the instructions listed here:

http://our.umbraco.org/wiki/install-and-setup/upgrading-an-umbraco-installation

I can no longer see any tree items on the left when logging into the Umbraco control panel on my local machine. When I look in the Event Viewer, I see the following:

Event code: 3005 
Event message: An unhandled exception has occurred. 
Event time: 8/30/2010 3:32:47 PM 
Event time (UTC): 8/30/2010 8:32:47 PM 
Event ID: a9163d5195624fcfaf2b582bd069178d 
Event sequence: 15 
Event occurrence: 1 
Event detail code: 0  

Application information: 

    Application domain: /LM/W3SVC/1/ROOT-7-129276739580731307 
    Trust level: Full 
    Application Virtual Path: / 
    Application Path: C:\Projects\UmbracoWebsite\
    Machine name: MYCOMPUTERNAME

Process information: 

    Process ID: 6044 
    Process name: aspnet_wp.exe 
    Account name: MYCOMPUTERNAME\ASPNET 

Exception information: 

    Exception type: HttpException 
    Exception message: The HTTP verb POST used to access path '/umbraco/webservices/TreeClientService.asmx/GetInitAppTreeData' is not allowed. 

Request information: 
    Request URL: http://localhost/umbraco/webservices/TreeClientService.asmx/GetInitAppTreeData ;
    Request path: /umbraco/webservices/TreeClientService.asmx/GetInitAppTreeData 
    User host address: 127.0.0.1 
    User:  
    Is authenticated: False 
    Authentication Type:  
    Thread account name: MYCOMPUTERNAME\ASPNET 

Thread information: 

    Thread ID: 32 
    Thread account name: MYCOMPUTERNAME\ASPNET 
    Is impersonating: False 

    Stack trace:    at System.Web.DefaultHttpHandler.BeginProcessRequest(HttpContext context, AsyncCallback callback, Object state)

   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()

   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Custom event details: 

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.