how do I debug this error message

I am getting the following error messages in my error log and have no idea how to debug the error. Application runs fine but everytime I run the app it writes this error message to the log file. Any ideas?

12/12/2008 14:49:23
Type : System.Web.HttpException, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
Message : File does not exist.
Source : System.Web
Help link :
ErrorCode : -2147467259
Data : System.Collections.ListDictionaryInternal
TargetSite : System.IO.FileInfo GetFileInfo(System.String, System.String, System.Web.HttpResponse)
Stack Trace :    at System.Web.StaticFileHandler.GetFileInfo(String virtualPathWithPathInfo, String physicalPath, HttpResponse response)
   at System.Web.StaticFileHandler.ProcessRequestInternal(HttpContext context)
   at System.Web.DefaultHttpHandler.BeginProcessRequest(HttpContext context, AsyncCallback callback, Object st ...