Creating and writing

You should not open the same file twice. By default, you open them with exclusive access, for a good reason. It would be really dangerous if you could have such dual access. There is not situations when you need to open it twice in the same program. If you still want it, stop wanting it — it will solve your problem.

Use just the StreamWriter; you don't need lower-level stream, but you can get underlying stream when you need it. [EDIT] Just use StreamWriter.BaseStream property. [END EDIT]

If you still don't see how to solve your problem with just one stream writer, please explain what do you want to achieve.

—SA

You are opening the same file twice. After openening/creating you have a stream which you can use for your writer.

Try this:

FileStream fs = new FileStream(@"C:\TestFile.txt", FileMode.Create);
TextWriter tw = new StreamWriter(fs);
            
tw.WriteLine("Test");
            
tw.Close();
fs.Close();