I'm running 2 different mojoPortal sites, one is 2.6.0.0 and one is 2.7.0.0.  On both, when I try to rebuild the search index it fails and gives several errors in the Windows event log.  I've tried various configurations of mapping log4net.dll versions within the web.config and cannot get it to work.  Here are the Windows messages:

An unhandled exception occurred and the process was terminated.

Application ID: /LM/W3SVC/2/ROOT

Process ID: 5200

Exception: System.IO.FileLoadException

Message: Could not load file or assembly 'log4net, Version=1.2.11.0, Culture=neutral, PublicKeyToken=1b44e1d426115821' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

StackTrace:    at WebStore.UI.Helpers.OfferSearchIndexBuilder.RebuildIndex(PageSettings pageSettings, String indexPath)
   at mojoPortal.SearchIndex.IndexHelper.RebuildSiteIndex(String indexPath, IEnumerable`1 menuPages)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
   at System.Threading.ThreadPoolWorkQueue.Dispatch()

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Exception information: 
    Exception type: HttpException 
    Exception message: Could not load file or assembly 'log4net, Version=1.2.13.0, Culture=neutral, PublicKeyToken=669e0ddf0bb1aa2a' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
   at System.Web.HttpApplicationFactory.EnsureAppStartCalledForIntegratedMode(HttpContext context, HttpApplication app)
   at System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers)
   at System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context)
   at System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context)
   at System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext)

Could not load file or assembly 'log4net, Version=1.2.13.0, Culture=neutral, PublicKeyToken=669e0ddf0bb1aa2a' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
   at mojoPortal.Web.Global.Application_Start(Object sender, EventArgs e)