In the TextBox Event Select TextChainged Event And then place this code there
Note:-Replace Textbox Name Here
string charactersAllowed = "0123456789";
string theText = TEXTBOXNAME.Text;
string Letter = null;
int SelectionIndex = TEXTBOXNAME.SelectionStart;
int Change = 0;
for (int x = 0; x <= TEXTBOXNAME.Text.Length - 1; x++) {
Letter = TEXTBOXNAME.Text.Substring(x, 1);
if (charactersAllowed.Contains(Letter) == false) {
theText = theText.Replace(Letter, string.Empty);
Change = 1;
}
}
TEXTBOXNAME.Text = theText;
TEXTBOXNAME.Select(SelectionIndex - Change, 0);
CHECK OUT This it Realy Works.....
All the Best ....