You have tagged your question
VB6 yet you appear to be trying to use
VB.NET constructs - ToString and DateInterval.Year.
I am going to assume that you are indeed using VB.NET - either way you will need to use the
IsDate
function
E.g.
Private Sub txtdateofBirth_Change()
If IsDate(txtcurrentDate.Text) Then
txtdateofBirth.Text = DateDiff(DateInterval.Year, Now, CDate(txtcurrentDate.Text)).ToString
End If
End Sub
or in VB6 probably
Private Sub txtdateofBirth_Change()
If IsDate(txtcurrentDate.Text) Then
txtdateofBirth.Text = Cstr(DateDiff(DateInterval.Year, Now, CDate(txtcurrentDate.Text)))
End If
End Sub
I also think you have
Now
and your textbox date in the wrong order