Hi Guys
I've made a id number textbox and wanna when users typing characters the server
tell them type digits
what should i do?

Why cant u try the Masked Edit control in Ajax Control Toolkit?

Or

Use CompareValidator using Type comparison.

Or

Manual Checking for ASCII - its not advisable.

use isnumeric

If (IsNumeric(TextBox1.Text)) Then
            MsgBox("correct")
        Else
            MsgBox("incorrect")
        End If

Use RegularExpressionValidator; which is used to determine whether the value of an input control matches the pattern defined by regular expression.

Validation exrpession for textbox that only accepts integer value is
^(?=.*[1-9].*$)\d{0,7}(?:\.\d{0,9})?$

Set ErrorMessage property to Enter digits Only or what ever you want.