c# - inserting smileys in RichTextBox inserts some and ignores others

I have a code to replace symbols in the richtextbox to smileys, this is the code:

private void add_smileys(RichTextBox addin)
        {
            try
            {
                while (addin.Text.Contains(":)"))
                {
                    addin.SelectionStart = addin.Find(":)", RichTextBoxFinds.WholeWord);
                    addin.SelectionLength = 2;

                    Image img = Resources.in_smile;
                    Clipboard.SetImage(img);
                    addin.Paste();
                }
                while (addin.Text.Contains(">:("))
                {
                    addin.SelectionStart = addin.Find(">:(", RichTextBoxFinds.WholeWord);
                    addin.SelectionLength = 3;

                    Image img = Resources.in_angry;
                    Clipboard.SetImage(img);
                    addin.Paste();
                }
                while (addin.Text.Contains(":D"))
                {
                    addin.SelectionStart = addin.Find(":D", RichTextBoxFinds.WholeWord);
                    addin.SelectionLength = 2;

                    Image img = Resources.in_lol;
                    Clipboard.SetImage(img);
                    addin.Paste();
                }
                while (addin.Text.Contains(":'("))
                {
                    addin.SelectionStart = addin.Find(":'(", RichTextBoxFinds.WholeWord);
                    addin.SelectionLength = 3;

                    Image img = Resources.in_cry;
                    Clipboard.SetImage(img);
                    addin.Paste();
                }
                while (addin.Text.Contains(":("))
                {
                    addin.SelectionStart = addin.Find(":(", RichTextBoxFinds.WholeWord);
                    addin.SelectionLength = 2;

                    Image img = Resources.in_sad;
                    Clipboard.SetImage(img);
                    addin.Paste();
                }
                while (addin.Text.Contains(";)"))
                {
                    addin.SelectionStart = addin.Find(";)", RichTextBoxFinds.WholeWord);
                    addin.SelectionLength = 2;

                    Image img = Resources.in_wink;
                    Clipboard.SetImage(img);
                    addin.Paste();
                }
                while (addin.Text.Contains("xD"))
                {
                    addin.SelectionStart = addin.Find("xD", RichTextBoxFinds.WholeWord);
                    addin.SelectionLength = 2;

                    Image img = Resources.in_laugh;
                    Clipboard.SetImage(img);
                    addin.Paste();
                }
                while (addin.Text.Contains(":P"))
                {
                    addin.SelectionStart = addin.Find(":P", RichTextBoxFinds.WholeWord);
                    addin.SelectionLength = 2;

                    Image img = Resources.in_tongue;
                    Clipboard.SetImage(img);
                    addin.Paste();
                }
                while (addin.Text.Contains(":|"))
                {
                    addin.SelectionStart = addin.Find(":|", RichTextBoxFinds.WholeWord);
                    addin.SelectionLength = 2;

                    Image img = Resources.in_neutral;
                    Clipboard.SetImage(img);
                    addin.Paste();
                }
                while (addin.Text.Contains("^^"))
                {
                    addin.SelectionStart = addin.Find("^^", RichTextBoxFinds.WholeWord);
                    addin.SelectionLength = 2;

                    Image img = Resources.in_happy;
                    Clipboard.SetImage(img);
                    addin.Paste();
                }
                while (addin.Text.Contains("o.O"))
                {
                    addin.SelectionStart = addin.Find("o.O", RichTextBoxFinds.WholeWord);
                    addin.SelectionLength = 3;

                    Image img = Resources.in_dizzy;
                    Clipboard.SetImage(img);
                    addin.Paste();
                }
                while (addin.Text.Contains(":S"))
                {
                    addin.SelectionStart = addin.Find(":S", RichTextBoxFinds.WholeWord);
                    addin.SelectionLength = 2;

                    Image img = Resources.in_confused;
                    Clipboard.SetImage(img);
                    addin.Paste();
                }
                while (addin.Text.Contains(":O"))
                {
                    addin.SelectionStart = addin.Find(":O", RichTextBoxFinds.WholeWord);
                    addin.SelectionLength = 2;

                    Image img = Resources.in_omg;
                    Clipboard.SetImage(img);
                    addin.Paste();
                }
            }
            catch (Exception e)
            {
              MessageBox.Show(e.Message);
            }
        }

and this is the output:

as you see, some symbols are replaced with smileys and some aren't. moreover, I get this exception:

What is the cause of this error? and how do I fix it? please be friendy and don't be mean. and don't be mean and don't downvote my Question, as I have been desparate about it for more than a week, please help me if you know the answer and don't ignore it.