Masked textbox

I think you need to validate the number when keypress event is triggered for the textbox.

Just use Javascript to do that :

function check_double(e,fieldid)
{
     var field = document.getElementById(fieldid);
     if (!(((e.keyCode>=48)&&(e.keyCode<=57))||(e.keyCode==46)))
     {
        e.returnValue = false;        
        e.keyCode=0;                   
     }     
     if (e.keyCode==46)
     {
        var patt1=new RegExp("\\.");        
        var ch =patt1.exec(field);       
        if(ch==".")
        {
            e.returnValue = false;
            e.keyCode=0;
        }                        
     }
} 

Now in your Page_Load use this :

TextBox.Attributes.Add("onkeypress", "javascript:check_double(event,'" + TextBox.ClientID + "');");

Just place this for every textbox for which you want to validate Double.

I hope you will like the solution.
Cheers
:rose: