Sharepoint - Cannot access document library files when logged in

I'm working on website where Sharepoint 2007 is being used as the CMS for a public facing site.

Internal users are authenticated via active directory and can edit content via an internal url. External users view the content via a public url. I've just added forms based authentication to the external facing version of the site in order to provide some special services to authenticated users.

The functionality works as expected on their dev servers but when rolled out to the test server any users authenticated via the forms based authentication are no longer able to access css files (which can be accessed via anonymous users). So all styling is lost. The CSS files are maintained in a document library. If the user is logged out these files become available again. (all via the external url and forms based authentication)

Any idea what might be going on?

Looking in the event logs provides the following information:

Event code: 3005 
Event message: An unhandled exception has occurred. 
Event time: 26/10/2010 3:08:20 p.m. 
Event time (UTC): 26/10/2010 2:08:20 a.m. 
Event ID: f6fbeb6ffe334e48aa150bc7d34aeda8 
Event sequence: 159 
Event occurrence: 29 
Event detail code: 0 

Application information: 
    Application domain: /LM/W3SVC/1334941635/ROOT-1-129325324099898564 
    Trust level: WSS_Minimal 
    Application Virtual Path: / 
    Application Path: E:\WebSites\test.company.co.nz\ 
    Machine name: INTERNETTEST 

Process information: 
    Process ID: 7616 
    Process name: w3wp.exe 
    Account 开发者_JS百科name: CH\InternetTestAPESite 

Exception information: 
    Exception type: FileNotFoundException 
    Exception message: The site with the id 5b06fc07-8611-4774-a283-7b9f94318030 could not be found. 

Request information: 
    Request URL: http://internettest.company.co.nz/Style Library/Company/CSS/base.css 
    Request path: /Style Library/Company/CSS/base.css 
    User host address: 172.23.4.119 
    User: gavin.harriss@somecompany.co.nz 
    Is authenticated: True 
    Authentication Type: Forms 
    Thread account name: CH\InternetTestAPESite 

Thread information: 
    Thread ID: 19 
    Thread account name: CH\InternetTestAPESite 
    Is impersonating: True 
    Stack trace:    at Microsoft.SharePoint.SPSite..ctor(Guid id, SPFarm farm, SPUrlZone zone, SPUserToken userToken)
   at Microsoft.SharePoint.SPSite..ctor(Guid id)
   at Microsoft.SharePoint.Publishing.BlobCache.<>c__DisplayClass3.<EnsureAuthenticatedRights>b__0()
   at Microsoft.SharePoint.SPSecurity.CodeToRunElevatedWrapper(Object state)
   at Microsoft.SharePoint.SPSecurity.<>c__DisplayClass4.<RunWithElevatedPrivileges>b__2()
   at Microsoft.SharePoint.Utilities.SecurityContext.RunAsProcess(CodeToRunElevated secureCode)
   at Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(WaitCallback secureCode, Object param)
   at Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(CodeToRunElevated secureCode)
   at Microsoft.SharePoint.Publishing.BlobCache.EnsureAuthenticatedRights(Guid siteID, Guid scopeID)
   at Microsoft.SharePoint.Publishing.BlobCache.RewriteUrl(Object sender, EventArgs e)
   at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

It was a blob caching issue. Clearing the cache followed by an iisreset resolved the issue.