Hi,

I have created a Custom Prevalue Type based on http://www.nibble.be/?p=86

    public class GetValuesFromMailChimp : FieldPreValueSourceType
    {
 
        public GetValuesFromMailChimp()
        {
            this.Id = new Guid("35C2053E-CBF7-4793-B27C-6E97B7671A2D");
            this.Name = "Get values from MailChimp";
            this.Description = "Getting values from MailChimp";
        }
 
        public override List<PreValue> GetPreValues(Field field)
        {
            List<PreValue> result = new List<PreValue>();
 
            try
            {            
                int sort = 0;
                string[] values = GetListSegments();
                foreach (string value in values)
                {
                    if (!string.IsNullOrEmpty(value.Trim()))
                    {
                        PreValue pv = new PreValue();
                        pv.Id = sort;
                        pv.Value = value;
                        if (field != null)
                        {
                            pv.Field = field.Id;
                        }
                        pv.SortOrder = sort;
                        result.Add(pv);
                        sort++;
                    }
                }
            }
            catch (Exception ex)
            {
                Umbraco.Forms.Data.LogHelper.Error(
                    "Get values from MailChimp: " + ex.ToString());
            }

            return result;
        }

        public override List<Exception> ValidateSettings()
        {
            List<Exception> exs = new List<Exception>();
                exs.Add(new Exception("No data from MailChimp"));
            return exs;
        }

       public string[] GetListSegments()
        {
            string strMailChimpURL = ConfigurationManager.AppSettings.Get(0);
            string strMailChimpAPIKey = ConfigurationManager.AppSettings.Get(1);
            string strMailChimpListID = ConfigurationManager.AppSettings.Get(2);
            string strMethod = "listInterestGroupings";
            MailChimpAPIRequest myPost = new MailChimpAPIRequest(strMailChimpURL, strMethod);
            myPost.Add("output", "xml");
            myPost.Add("apikey", strMailChimpAPIKey);
            myPost.Add("id", strMailChimpListID);
            string strMailChimpResponse = myPost.GetResponse();
            System.Xml.XmlDocument doc = new System.Xml.XmlDocument();
            doc.LoadXml(strMailChimpResponse);
            XmlNodeList nodes = doc.SelectNodes("//groups/struct");
            string strTest = "";
            foreach (XmlNode node in nodes)
            {
                strTest = strTest + node["name"].InnerText + "|";
            }

            string[] selectedValues = strTest.Split("|".ToCharArray(), StringSplitOptions.RemoveEmptyEntries);
            return selectedValues;
        }
    }

When I select it from the Type dropdown, the Preview works fine.

But when I click on SAVE, it says there is a problem with the Settings?

Any help much appreciated.