>>>>Thank you for both replies. What happens is that if the value of @TargetDate is NULL, all works.
>>>>Or if the value of @TargetDate from the XML type is American format (that works for many customers), all works.
>>>>But when I set the value in the ASP.NET application to the XML element TargetDate, I get error.
>>>>Why I do it this way is a long story. But it works for many years.
>>>>Now I need to figure where it breaks for the British date.
>>>
>>>"if the value of @TargetDate from the XML type is American format" - That is what I am saying, in the XML the format for a DateTime is fixed, regardless you are living in US or Turkey, or choose any place you like. It is like:
>>>
>>>2019-02-28T19:00:00+03:00
>>>
>>>I don't understand what does XML datetime have to do with ToShortTimeString(). Are you sure your XML is defining a DateTime type?
>>
>>How do I convert a date (in the ASP.NET) into the format you described (above).
>>For example if I get the date value, as follows:
>>

>>DateTime TargetDate = DateTime.Now;
>>

>>How do I convert it to a string of the format "2019-02-28T19:00:00+03:00"?
>
>That is the point, you don't convert that to a string. XML serializers do that for you, you don't have to do anything special but simply keep it as a DateTime rather than a string. ie:
>
>

>void Main()
>{
>  List<Product> myProducts = new List<Product> {
>     new Product { SKU="108.100.123", ListPrice=22, Price=16, CurrencyType="TRL", EffectiveFrom = DateTime.Now},
>  };
>  XNamespace ns = "urn:my-scripts";
>  XDocument doc = new XDocument( 
>      new XDeclaration("1.0","utf-8",""),
>      new XElement("Products",
>        new XAttribute(XNamespace.Xmlns+"user",ns),
>          from p in myProducts
>          select new XElement("Product",
>                    new XElement("SKU", p.SKU),
>                    new XElement("ListPrice", p.ListPrice),
>                    new XElement("Price", p.Price),
>					new XElement("CurrencyType", p.CurrencyType),
>					new XElement("EffectiveFrom", p.EffectiveFrom)
>					)
>        )           
>  );
>  
>  var xml = new StringBuilder();
>  using (XmlWriter xw = XmlWriter.Create (xml, new XmlWriterSettings { Indent = true }))
>  {
>	  doc.Save (xw);
>  }
>  string sonuc = xml.ToString();
>  Console.WriteLine (sonuc);
>}
>
>public class Product
>{
>  public string SKU { get; set; }
>  public decimal ListPrice { get; set; }
>  public decimal Price { get; set; }
>  public string CurrencyType { get; set; }
>  public DateTime? EffectiveFrom { get; set; }
>}
>

>
>
>And the output is:
>
>

><?xml version="1.0" encoding="utf-16"?>
><Products xmlns:user="urn:my-scripts">
>  <Product>
>    <SKU>108.100.123</SKU>
>    <ListPrice>22</ListPrice>
>    <Price>16</Price>
>    <CurrencyType>TRL</CurrencyType>
>    <EffectiveFrom>2019-02-07T22:13:42.27652+03:00</EffectiveFrom>
>  </Product>
></Products>
>

My code does not use the XML serializer. And I cannot change the code - now - just for this case. So, I will have to find a solution still.
Thank you.