server/AyaNova/biz/FormAvailableFields.cs

@@ -100,7 +100,12 @@ namespace AyaNova.Biz
 
         public static string TranslateLTCustomFieldToInternalCustomFieldName(string lTCustomFieldName)
         {
-            var i = int.Parse(lTCustomFieldName);
+            var i = System.Convert.ToInt32(System.Text.RegularExpressions.Regex.Replace(
+                        lTCustomFieldName,  // Our input
+                        "[^0-9]", // Select everything that is not in the range of 0-9
+                        ""        // Replace that with an empty string.
+                    ));
+
             return $"c{i}";
         }