Dmitry,

I find the easiest way to validate a field in ASP.NET is to use a WebControl validator. For example, if you wanted to validate the date field is formatted correctly then you would use a text control associate a control based on the following class.

protected System.Web.UI.WebControls.TextBox CompletionDate;
protected System.Web.UI.WebControls.CompareValidator CompletionDateCompareValidator;

The CompareValidator control supports the following properties:-

Type=Date
ErrorMessage=Date format is incorrect
ControlToValidate=CompletionDate
Operator=DateTypeCheck

Once you need the value as a System.DateTime type then you can convert the contents as the value should be validated correctly.

Convert.ToDateTime(CompletionDate.Text)

I am by no means an ASP.NET expert but this seems to work for my limited requirements.

Regards
Neil