Does anyone have any ideas on this? I'm really stuck. Here is the
callstack output  I get, if it helps:

File Not Found. at Microsoft.SharePoint.SPSite..ctor(SPFarm farm,
Uri requestUri, Boolean contextSite, SPUserToken userToken)
at
Microsoft.SharePoint.Administration.SPNativeConfigurationProvider.Look
upSite(String requestUrl, Int32 iisInstanceId, String& siteUrl,
Int32& zone, Guid& appId, Guid& siteId, Guid& databaseId, String&
databaseServer, String& databaseName, String& databaseUsername,
String& databasePassword, Boolean& useHostHeaderForSiteName)
at Microsoft.SharePoint.Library.SPRequestInternalClass.CreateWeb
(String bstrUrl, String bstrTitle, String bstrDescription, UInt32
nLCID, String bstrWebTemplate, Boolean bCreateUniqueWeb, Boolean
bConvertIfThere, Guid& pgWebId, Guid& pgRootFolderId, Boolean
bCreateSystemCatalogs)
at Microsoft.SharePoint.Library.SPRequest.CreateWeb(String
bstrUrl, String bstrTitle, String bstrDescription, UInt32 nLCID,
String bstrWebTemplate, Boolean bCreateUniqueWeb, Boolean
bConvertIfThere, Guid& pgWebId, Guid& pgRootFolderId, Boolean
bCreateSystemCatalogs)
at Microsoft.SharePoint.SPWeb.CreateWeb(String strWebUrl, String
strTitle, String strDescription, UInt32 nLCID, String strWebTemplate,
Boolean bCreateUniqueSubweb, Boolean bConvertIfThere)
at Microsoft.SharePoint.SPWeb.SPWebCollectionProvider.CreateWeb
(String strWebUrl, String strTitle, String strDescription, UInt32
nLCID, String strWebTemplate, Boolean bCreateUniqueSubweb, Boolean
bConvertIfThere)
at Microsoft.SharePoint.SPWebCollection.Add(String strWebUrl,
String strTitle, String strDescription, UInt32 nLCID, String
strWebTemplate, Boolean useUniquePermissions, Boolean
bConvertIfThere)
at Microsoft.SharePoint.SPWebCollection.Add(String strFullWebUrl,
String strWebUrl, String strTitle, String strDescription, UInt32
nLCID, String strWebTemplate, Boolean useUniquePermissions, Boolean
bConvertIfThere)
at
Microsoft.SharePoint.ApplicationPages.NewSubwebPage.BtnCreateSubweb_Cl
ick(Object sender, EventArgs e)
at System.Web.UI.WebControls.Button.OnClick(EventArgs e)
at System.Web.UI.WebControls.Button.RaisePostBackEvent(String
eventArgument)
at
System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.R
aisePostBackEvent(String eventArgument)
at System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler
sourceControl, String eventArgument)
at System.Web.UI.Page.RaisePostBackEvent(NameValueCollection
postData)
at System.Web.UI.Page.ProcessRequestMain(Boolean
includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)