enum_in.Single() is 1 and throws exception
===

I m executing the follwing code: 

    private static T FooException<T>( this IEnumerable<T> enum_in )
    
          {
    
                try
    
                {
    
                    return enum_in.Single();
    
                }
    
                catch( InvalidOperationException e )
    
                {
    
    
                    throw new XXXException(  enum_in.Count(),  e   ...
    
    
                }
    
    
    }

 and getting an  InvalidOperationException.
But if I have a look at enum.Count() then ther is exactly one item.
Thats what I don't understand. Are there any cases where the enum can be with count = 1
and running in InvalidOperationException ?



