VbScript Form Validations

Hi,
In Form Validations i have used the following code:-

If IsNumeric(txtJobCode.Text) Then
If txtJobCode.Text < 100 Or txtJobCode.Text > 174 Then
MsgBox "Please enter a number for JOBCODE between 100 and 174 only."
End If
txtJobCode.SetFocus
End If

So my problem is that my textbox which is txtJobCode does not get the setfocus again and so i get a vbScript error. I do get the my form validation MsgBox "Please enter a number for JOBCODE between 100 and 174 only." no doubt....... but the text box never gets the focus again.
How do i do this????????
Thanks in advance,
New to VB......