log4net.Appender.MemoryAppender.GetEvents() excption

log4net.Appender.MemoryAppender.GetEvents() excption

   在 System.Collections.ArrayList.ToArray(Type type)
   在 log4net.Appender.MemoryAppender.GetEvents()
     在 System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   在 System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   在 System.Threading.ThreadHelper.ThreadStart() 

 lock (MemoryAppender){
    MemoryAppender.GetEvents()
   MemoryAppender.clear()
 }