CSL_Test__1.OptionsWindow.CustomFolderTextbox_Validating C# (CSharp) Method

        private void CustomFolderTextbox_Validating(object sender, CancelEventArgs e)
        {
            bool error = false;
            Match m;
            char[] chararray = CustomFolderTextbox.Text.ToCharArray();
            string letter;

                for (int a = 0; a < chararray.Length; a++)
                {
                    if (chararray[a] == '%')
                    {
                        try
                        {
                            letter = chararray[++a].ToString();

                            m = Regex.Match(letter, "a|l|s|c|e|r|v|n|x|u|y|t|i|b|p|d|z");
                            if (!m.Success)
                            {
                                ErrorProvider.SetError(this.CustomFolderTextbox, "Invalid letter after switch");
                                error = true;
                            }
                        }
                        catch { }
                    }
                }

            if (!error)
                ErrorProvider.Clear();
        }