IIS problem with ASP.NET

Good I leave you the errors that I visualize in the viewer of events:

Error 1

Exception : The server was unable to process the request due to an internal error.  For more information about the error, either turn on IncludeExceptionDetailInFaults (either from ServiceBehaviorAttribute or from the <serviceDebug> configuration behavior) on the server in order to send the exception information back to the client, or turn on tracing as per the Microsoft .NET Framework SDK documentation and inspect the server trace logs.

Error 2

An unhandled exception occurred and the process was terminated.

Application ID: /LM/W3SVC/2/ROOT

Process ID: 6972

Exception: System.IndexOutOfRangeException

Message: Index was outside the bounds of the array.

StackTrace:    at System.Collections.ArrayList.Add(Object value)
   at log4net.Util.LogReceivedEventHandler.Invoke(Object source, LogReceivedEventArgs e)
   at log4net.Util.LogLog.OnLogReceived(Type source, String prefix, String message, Exception exception)
   at log4net.Appender.AppenderSkeleton.Finalize()

Error 3

An unhandled Microsoft .NET Framework exception occurred in w3wp.exe [6972]. Just-In-Time debugging this exception failed with the following error: Debugger could not be started because no user is logged on.

Check the documentation index for 'Just-in-time debugging, errors' for more information.

Appenders log4net:

 <log4net debug="true">
    <appender name="RollingLogFileAppender" 
        type="log4net.Appender.RollingFileAppender">

      <file value="backend-end-log.txt" />
      <appendToFile value="true" />
      <datePattern value="yyyyMMdd" />

      <rollingStyle value="Date" />
      <filter type="log4net.Filter.LevelRangeFilter">
        <acceptOnMatch value="true" />

        <levelMin value="DEBUG" />
        <levelMax value="FATAL" />
      </filter>
      <maximumFileSize value="100MB" />

      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%-5p %d %5rms %-22.22c{1} %-18.18M - %m%n" />
      </layout>

    </appender>

    <root>
      <level value="DEBUG" />
      <appender-ref ref="RollingLogFileAppender" />
    </root>

  </log4net>

The app fails and returns these errors to me.

Thanks again.

Greetings.