How to fix ''System.ArgumentException" in c#?

I'm working on a small project that involves compiling code. I keep getting this error: An unhandled exception of type 'System.ArgumentException' occurred in mscorlib.dll Illegal characters in path.

I've tried finding the source of the problem, this line of code seems to be the problem: CompilerResults cr = provider.CompileAssemblyFromFile(parameters, source1);

This is my code for my class:

using System.IO;
using Microsoft.CSharp;
using System.CodeDom.Compiler;


namespace Plugin___Prototype
{
    class CompileCode
    {
        public void Compile()
        {
            string source1 = File.ReadAllText(System.Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments) + @"\test.cs");
            //string source2 = File.ReadAllText(@"Source path here");
            Console.WriteLine(source1);
            CSharpCodeProvider provider = new CSharpCodeProvider();
            CompilerParameters parameters = new CompilerParameters();
            parameters.ReferencedAssemblies.Add("System.dll");
            parameters.GenerateExecutable = true;
            parameters.OutputAssembly = System.Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments) + @"\app1.exe";
            Console.WriteLine(parameters.OutputAssembly);
            parameters.GenerateInMemory = false;
            CompilerResults cr = provider.CompileAssemblyFromFile(parameters, source1);

            if (cr.Errors.Count == 0)
                Console.WriteLine("No Errors");
            else
            {
                foreach (CompilerError error in cr.Errors)
                    Console.WriteLine(error.ErrorText);
            }

            Console.ReadLine();
        }
    }
}

This is the output:

An unhandled exception of type 'System.ArgumentException' occurred in mscorlib.dll
Illegal characters in path.

The program '[14128] Plugin - Prototype.exe' has exited with code -1 (0xffffffff). 

My expected result is for app1.exe to generated in my documents folder.

EDIT: These are the contents of source1:

// A Hello World! program in C#.
using System;
namespace HelloWorld
{
    class Hello
    {
        static void Main()
        {
            Console.WriteLine("Hello World!");

            // Keep the console window open in debug mode.
            Console.WriteLine("Press any key to exit.");
            Console.ReadKey();
        }
    }
}

I've fixed it, CompilerResults cr = provider.CompileAssemblyFromFile(parameters, source1);, wanted the file not the contents of the file.