I have run into issue when set up IIS 7 Farm for Load balancing. Add 4 server to IIS Farm with appropriate ports(8080,8081,8082,8083). Also add Inbound rule for IIS Farm. The Tomcat instances listens these ports. When i'm opening url(which i set on inbound rule), i got the following exception:

The virtual path 'null' maps to another application, which is not allowed.     
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:     
[ArgumentException: The virtual path 'null' maps to another application, which is not allowed.]
   System.Web.CachedPathData.GetVirtualPathData(VirtualPath virtualPath, Boolean permitPathsOutsideApp) +8839122
   System.Web.HttpContext.GetFilePathData() +36
   System.Web.HttpContext.GetConfigurationPathData() +26
   System.Web.Configuration.RuntimeConfig.GetConfig(HttpContext context) +43
   System.Web.Configuration.CustomErrorsSection.GetSettings(HttpContext context, Boolean canThrow) +41
   System.Web.HttpResponse.ReportRuntimeError(Exception e, Boolean canThrow, Boolean localExecute) +101
   System.Web.HttpContext.ReportRuntimeErrorIfExists(RequestNotificationStatus& status) +538

How can i solve this issue?