wordpress XMLRC metaWebBlog custom field issue

Hello,
I want to post articles to my blog from a C# desktop application. For this i am using XMLRC. The code without the custom fields is working fine.

I will be thankful if you can help me solving the following: 1- Why the code that i wrote for custom fields in not working ? I want to set the All In One SEO pack plugin fields.

2- How can i attach Featured Image ?

Following is my code:

public interface IgetCatList
{
    [CookComputing.XmlRpc.XmlRpcMethod("metaWeblog.newPost")]
    string NewPage(int blogId, string strUserName, string strPassword, blogInfo content, int publish);

    [XmlRpcMethod("metaWeblog.newMediaObject", Description = "Add a media object to a post using the metaWeblog API. Returns media url as a string.")]
    MediaObjectUrl newMediaObject(int blogid,string username,string password,MediaObject mediaObject);
}

public struct customField
{
    public string key;
    public string value;
}

public struct blogInfo
{
    public string title;
    public string description;
    public string post_type;
    public string[] categories;
    public string mt_keywords;
    public string mt_excerpt;
    public customField[] custom_fields;
}

private void PostToBlogUsingXMLRC(string pTitle,string pPost)
    {

        blogInfo newBlogPost = default(blogInfo);

        newBlogPost.title = pTitle;
        newBlogPost.description = pPost;
        newBlogPost.categories = new string[] { "TechReviews" };
        newBlogPost.post_type = "post";
        newBlogPost.mt_excerpt = "this is excerpt";
        newBlogPost.mt_keywords = "keywrod";
        //aiosp
        //aioseop
        customField aioseoTitle = default(customField);
        aioseoTitle.key = "_aioseop_title";
        aioseoTitle.value = "This is SEO Title";

        customField aioseoDesc = default(customField);
        aioseoDesc.key = "_aioseop_description";
        aioseoDesc.value = "This is SEO description";

        customField aioseoKeyword = default(customField);
        aioseoKeyword.key = "_aioseop_keywords";
        aioseoKeyword.value = "This is SEO keywords";

        //customField thumbnailImage = default(customField);
        //thumbnailImage.key = "_thumbnail_id";
        //thumbnailImage.value= PostNewMediaObject();

        newBlogPost.custom_fields = new customField[] { aioseoTitle, aioseoDesc, aioseoKeyword };

        categories = (IgetCatList)XmlRpcProxyGen.Create(typeof(IgetCatList));
        clientProtocol = (XmlRpcClientProtocol)categories;

        clientProtocol.Url = "https://abc.com/xmlrpc.php";

        string result = null;
        result = "";

        try
        {
            result = categories.NewPage(1, "ID", "Pass", newBlogPost, 1);

            MessageBox.Show("Posted to Blog successfullly! Post ID : " + result);
            pTitle = "";
            pPost = "";
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
    }