private static AppDomain GetDomainForGenerator()
{

AppDomainSetup setup = new AppDomainSetup();
setup.ApplicationName = "ASP.NET Generator";

AppDomain dom = AppDomain.CreateDomain("generator domain" , null, setup);

dom.SetData(".appPath", Directory.GetCurrentDirectory() +
Path.DirectorySeparatorChar);
dom.SetData(".appDomain", "*");
dom.SetData(".appVPath", "/");
dom.SetData(".domainId", dom.FriendlyName);
dom.SetData(".hostingVirtualPath", "/");
dom.SetData(".hostingInstallDir", HttpRuntime.AspInstallDirectory);

return dom;
}

[NullReferenceException: Object reference not set to an instance of an object.]
System.Web.CachedPathData.GetPathData(String path) +363
System.Web.CachedPathData.GetPathData(String path) +275
System.Web.HttpContext.GetFilePathData() +26
System.Web.HttpContext.GetConfigPathData() +16
System.Web.Configuration.CustomErrorsSection.GetSettings(HttpContext context, Boolean canThrow) +89
System.Web.HttpResponse.ReportRuntimeError(Exception e, Boolean canThrow, Boolean localExecute) +98
System.Web.HttpRuntime.FinishRequest(HttpWorkerRequest wr, HttpContext context, Exception e) +438