Very unusual problem when deploying IIS apps

Could not load type 'RequestModule'.

[HttpException (0x80004005): Could not load type 'RequestModule'.]
   System.Web.Compilation.BuildManager.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase) +11532169
   System.Web.Configuration.ConfigUtil.GetType(String typeName, String propertyName, ConfigurationElement configElement, XmlNode node, Boolean checkAptcaBit, Boolean ignoreCase) +76

[ConfigurationErrorsException: Could not load type 'RequestModule'.]
   System.Web.Configuration.ConfigUtil.GetType(String typeName, String propertyName, ConfigurationEleme开发者_如何学Gont configElement, XmlNode node, Boolean checkAptcaBit, Boolean ignoreCase) +11472060
   System.Web.Configuration.Common.ModulesEntry.SecureGetType(String typeName, String propertyName, ConfigurationElement configElement) +69
   System.Web.Configuration.Common.ModulesEntry..ctor(String name, String typeName, String propertyName, ConfigurationElement configElement) +62
   System.Web.HttpApplication.BuildIntegratedModuleCollection(List`1 moduleList) +264
   System.Web.HttpApplication.GetModuleCollection(IntPtr appContext) +1356
   System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers) +149
   System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context) +352
   System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) +407
   System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) +375

[HttpException (0x80004005): Could not load type 'RequestModule'.]
   System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +11642112
   System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +141
   System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +4865877

Any suggestions?

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I think either your IIS is set to the wrong version of the framework, or your machine config is corrupt.

Check framework first then try a different machine with same set up. This is assuming your web.configs are all OK.