System.IO.IOException: The process cannot access the file encoded.txt because it Is being used by another process

Question

It says that its being used already, but it's being used by a stream reader, and a stream writer. I dont know what it wants me to do, I tried creating the file to no avail still gave me an error.

using System;
using System.IO;

namespace EncoderDecoder
{ 
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(compressor());
            decoder(compressor());
            Console.WriteLine(compare());

        }
        static string compressor()
        {
            string[] lines = System.IO.File.ReadAllLines(@"panda-small.txt");
            string set = "0";
            int count = 0;
            string encoded = "";
            foreach(string Line in lines)
            {
                for (int i = 0; i < Line.Length; i++)
                {
                    if (Line.Substring(i, 1) == set)
                    {
                        count++;
                    }
                    else
                    {
                        encoded += count;
                        encoded += ",";
                        count = 0;
                        if (set == "0")
                        {
                            set = "1";
                            count++;
                        }
                        else
                        {
                            set = "0";
                            count++;
                        }
                    }
                }
            }
            encoded += count;
            return encoded;
        }

        static void decoder(string encoded)
        {
            File.Create("encoder.txt");
            StreamWriter writer = new StreamWriter("encoded.txt");
            string line = "";
            string[] decoderArr = encoded.Split(",");
            string set = "0";
            int count = 0;
            for(int i = 0; i < decoderArr.Length; i++)
            {
                if(decoderArr[i] == "ln" || decoderArr[i] == "")
                {
                    Console.Write(Environment.NewLine);
                }
                else
                {
                    for (int j = 0; j < Convert.ToInt32(decoderArr[i]); j++)
                    {  
                        if(count == 35)
                        {
                            Console.WriteLine();
                            count = 0;
                            writer.WriteLine(line);
                            line = "";
                        }
                        count++;
                        line += set;
                        Console.Write(set);
                    }
                    if (set == "0")
                    {
                        set = "1";
                    }
                    else
                    {
                        set = "0";
                    }
                }
            }
        }

        static string compare()
        {
            StreamReader sr = new StreamReader("panda-small.txt");
            StreamReader sr1 = new StreamReader("encoded.txt");
            if (sr == sr1)
            {
                return "true";
            }
            return "false";
        }
    }
}