How to handle validation errors in vbscript?

How to handle validation errors to string in vbscript? I don't understand why if I type a letter my code doesn't return to the loop

Dim mark
Dim ask
mark = Chr(10) & "   " & Chr(149) & " "

Do

    ask = InputBox("Select:" & Chr(10) & mark & "1) First" & mark & "2) Second" & mark & "3) All" & Chr(10), "Select a option")
    If IsEmpty(ask) Then WScript.Quit  'Read if canceled
    If IsNumeric(ask) and CStr(CLng(ask)) = ask and ask => 1 and ask <= 3 Then Exit Do
    MsgBox "Choice a valid value", 48, "Ops..."
Loop