Incorrect ApplicationMasterModule

At the customer I’m working a strange thing happened. In the intranet farm (4 WFE loadbalanced with NLB) on two of the WFE servers going to Site Actions > All Site Settings resulted in the following error:

File not found. at Microsoft.SharePoint.ApplicationRuntime.SPRequestModuleData.GetWebPartPageData(HttpContext context, String path, Boolean throwIfFileNotFound)
   at Microsoft.SharePoint.ApplicationRuntime.SPVirtualFile.GetVirtualPathProviderCacheKey(String virtualPath)
   at Microsoft.SharePoint.ApplicationRuntime.SPVirtualPathProvider.GetCacheKey(String virtualPath)
   at Microsoft.SharePoint.Publishing.Internal.CmsVirtualPathProvider.GetCacheKey(String virtualPath)
   at System.Web.Compilation.BuildManager.GetCacheKeyFromVirtualPath(VirtualPath virtualPath, Boolean& keyFromVPP)
   at System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile)
   at System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile)
   at System.Web.UI.MasterPage.CreateMaster(TemplateControl owner, HttpContext context, VirtualPath masterPageFile, IDictionary contentTemplateCollection)
   at System.Web.UI.Page.get_Master()
   at System.Web.UI.Page.ApplyMasterPage()
   at System.Web.UI.Page.PerformPreInit()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

The two WFE servers are also the two oldest WFE servers in the farm. The other two have been added must later to the farm. These last two I added myself (so they are installed correct ). I searched the internet for some solution and found this post at the technet forum:

http://social.technet.microsoft.com/Forums/en/sharepointadmin/thread/172778d8-e1b6-4959-934d-fa65ac88b799

Here the given solution was to copy the 12hive to the WFE servers with the errors. This solution did not work for me.

Solution
The solution was to compare the web.config files between the older and newer WFE servers. Finally I saw that the following HttpModule that caused all the trouble. By removing this line it all worked:

<HttpModules>
   <add name="xxxxApplicationMaster"
        type="xxxx.SharePoint.yyyy.HttpModules.ApplicationMasterModule,
              xxxx.SharePoint.yyyy.HttpModules,
              Version=1.0.0.0,
              Culture=neutral,
              PublicKeyToken=f7b60d01076d3308" />
</HttpModules>

Tags: error, web.config