All of a sudden my dnn started to become very slow and even ended up in an error message "Server too busy".

I've restarted the IIS several times now (in fact my hoster), played a little bit and figured that simply opening my start page causes at least 130 event logs and all of them are SCHEDULER_EXCEPTIONs or GENERAL_EXCEPTIONs. 

I don't want to post all of them here, just two :

SCHEDULER_EXCEPTION
<LogProperties><LogProperty><PropertyName>AssemblyVersion</PropertyName><PropertyValue>-1</PropertyValue></LogProperty><LogProperty><PropertyName>PortalID</PropertyName><PropertyValue>-1</PropertyValue></LogProperty><LogProperty><PropertyName>PortalName</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>UserID</PropertyName><PropertyValue>-1</PropertyValue></LogProperty><LogProperty><PropertyName>UserName</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>ActiveTabID</PropertyName><PropertyValue>-1</PropertyValue></LogProperty><LogProperty><PropertyName>ActiveTabName</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>RawURL</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>AbsoluteURL</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>AbsoluteURLReferrer</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>UserAgent</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>DefaultDataProvider</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>ExceptionGUID</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>InnerException</PropertyName><PropertyValue>Der Thread wurde abgebrochen.</PropertyValue></LogProperty><LogProperty><PropertyName>FileName</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>FileLineNumber</PropertyName><PropertyValue>-1</PropertyValue></LogProperty><LogProperty><PropertyName>FileColumnNumber</PropertyName><PropertyValue>-1</PropertyValue></LogProperty><LogProperty><PropertyName>Method</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>StackTrace</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>Message</PropertyName><PropertyValue>System.Threading.ThreadAbortException: Der Thread wurde abgebrochen.
   bei System.Threading.ReaderWriterLock.AcquireReaderLockInternal(Int32 millisecondsTimeout)
   bei DotNetNuke.Services.Scheduling.DNNScheduling.Scheduler.CoreScheduler.IsInQueue(ScheduleItem objScheduleItem)
   bei DotNetNuke.Services.Scheduling.DNNScheduling.Scheduler.CoreScheduler.LoadQueueFromTimer()
   bei DotNetNuke.Services.Scheduling.DNNScheduling.Scheduler.CoreScheduler.Start()</PropertyValue></LogProperty><LogProperty><PropertyName>Source</PropertyName><PropertyValue /></LogProperty></LogProperties>

GENERAL_EXCEPTION
<LogProperties><LogProperty><PropertyName>AssemblyVersion</PropertyName><PropertyValue>-1</PropertyValue></LogProperty><LogProperty><PropertyName>PortalID</PropertyName><PropertyValue>-1</PropertyValue></LogProperty><LogProperty><PropertyName>PortalName</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>UserID</PropertyName><PropertyValue>-1</PropertyValue></LogProperty><LogProperty><PropertyName>UserName</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>ActiveTabID</PropertyName><PropertyValue>-1</PropertyValue></LogProperty><LogProperty><PropertyName>ActiveTabName</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>RawURL</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>AbsoluteURL</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>AbsoluteURLReferrer</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>UserAgent</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>DefaultDataProvider</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>ExceptionGUID</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>InnerException</PropertyName><PropertyValue>Der Typ "" konnte nicht geladen werden.</PropertyValue></LogProperty><LogProperty><PropertyName>FileName</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>FileLineNumber</PropertyName><PropertyValue>-1</PropertyValue></LogProperty><LogProperty><PropertyName>FileColumnNumber</PropertyName><PropertyValue>-1</PropertyValue></LogProperty><LogProperty><PropertyName>Method</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>StackTrace</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>Message</PropertyName><PropertyValue>System.Web.HttpException: Der Typ "" konnte nicht geladen werden. ---&gt; System.ArgumentException: Die Zeichenfolge kann keine Länge von 0 (null) haben.
   bei System.Reflection.Assembly.GetType(String name, Boolean throwOnError, Boolean ignoreCase)
   bei System.Web.Compilation.BuildManager.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase)
   --- Ende der internen Ausnahmestapelüberwachung ---
   bei System.Web.Compilation.BuildManager.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase)
   bei DotNetNuke.Framework.Reflection.CreateType(String TypeName, String CacheKey, Boolean UseCache, Boolean IgnoreErrors)</PropertyValue></LogProperty><LogProperty><PropertyName>Source</PropertyName><PropertyValue /></LogProperty></LogProperties>

I am running DNN 04.05.03.

This happended all of a sudden without any changes.

Any ideas anyone ?

Regards, Tom.

Are you still using xml file's to log, if the xml file grows too large it can cause problems. If so I recommend you change the provider in the web.config, it should look something like this (i've bolded the key part). Secondly the second error is around a missing type. This means a class can't be instantiated, which typically means a dll file containing that definiton is missing. Please check you bin folder and ensure no dll files have been deleted by mistake.

  <logging
      defaultProvider="DBLoggingProvider">
      <providers>
        <clear/>
        <add
          name="XMLLoggingProvider"
          type="DotNetNuke.Services.Log.EventLog.XMLLoggingProvider, DotNetNuke.XMLLoggingProvider"
          configfilename="LogConfig.xml.resources"
          providerPath="~\Providers\LoggingProviders\XMLLoggingProvider\"/>
        <add
          name="DBLoggingProvider"
          type="DotNetNuke.Services.Log.EventLog.DBLoggingProvider.DBLoggingProvider, DotNetNuke.Provider.DBLoggingProvider"
          providerPath="~\Providers\LoggingProviders\Provider.DBLoggingProvider\"/>
      </providers>
    </logging>