在创建一个iCal文件时，我没有处理什么

关于我的问题，我在阅读文件时做得对吗?

我正在使用这个代码来创建一个iCal文件，但不确定我是否做得对，或者需要处理任何得到这个错误，

System.IO.IOException: The process cannot access the file 'C:'doc.ics' because it is being used by another process.
   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
   at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy)
   at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options)
   at System.IO.StreamWriter.CreateFile(String path, Boolean append)
   at System.IO.StreamWriter..ctor(String path, Boolean append, Encoding encoding, Int32 bufferSize)
   at System.IO.StreamWriter..ctor(String path)

我使用的代码是

    String filePath = paramUri.LocalPath.ToString().TrimStart("filePath:///".ToCharArray());
    int lastSlash = filePath.LastIndexOf('''');
    if(lastSlash > 0)
    {
        String folderPath = filePath.Substring(0, lastSlash);
        DirectoryInfo di = new DirectoryInfo(folderPath);
        if(!di.Exists)
            di.Create();
    }
    //Use a streamwriter to create a file in the location specified in the URI
    using (StreamWriter sw = new StreamWriter(filePath))
    {
        //Autoflush enabled so we don't have to worry about closing the streamwriter
        sw.AutoFlush = true;
        sw.WriteLine("BEGIN:VCALENDAR");
        sw.WriteLine("PRODID:-//Microsoft Corporation//Outlook 12.0 MIMEDIR//EN");
        sw.WriteLine("VERSION:2.0");
        sw.WriteLine("METHOD:PUBLISH");
        sw.WriteLine("X-MS-OLK-FORCEINSPECTOROPEN:TRUE");
        //I am adding more details but they are not relevant to post
    }