Error : “The process cannot access the file ''

Question

 This is my code. Could you please anyone tell me the reason for the error which i mentioned. Using statement usually dispose the object once it went out of scope, but i am getting the error.

public static void WriteLogFile(string message)
        {
            Console.WriteLine(message);

            if (File.Exists("C:\\log.txt"))
            {
                using (StreamWriter SWriter = File.AppendText("C:\\log.txt"))
                {
                    SWriter.WriteLine(message);
                }
            }
            else
            {
                using (StreamWriter SWriter = File.CreateText("C:\\log.txt"))
                {
        
                    SWriter.WriteLine(message);
                }
            }
        }