i'm having trouble decrypting an encrypted text file and saving it into an output file. The error that i got was "PKCS7 padding is invalid and cannot be removed."

I'm wondering what's wrong with my code.

FileStream fsIn = File.Open(file,FileMode.Open,FileAccess.Read);
        FileStream fsOut = File.Open(tempfile, FileMode.OpenOrCreate,FileAccess.Write);
ICryptoTransform transform = symm.CreateDecryptor();
        CryptoStream cstream = new CryptoStream(fsOut,transform,CryptoStreamMode.Writ e);
        BinaryReader br = new BinaryReader(fsIn);
        cstream.Write(br.ReadBytes((int)fsIn.Length),0,(in t)fsIn.Length);

        cstream.FlushFinalBlock();
        cstream.Close();
fsIn.Close();
         fsOut.Close();