Hello all, easy problem I hope!

Private Sub Worksheet_Calculate()
If Range("R3") <> Range("R1") Then Range("M13") = "BOOOOOH!"
End Sub
R1 is from a formula, R3 is data I enter.

When I change R3 by typing in a value, the macro works.

When R3 gets changed by a scroll bar (form controls), it does not work, and gives me a "Application defined or object defined error 50290"..

It is as if Excel has to 'exit' from this form control thing and go back to its usual duties.. Does anyone have a sollution to this?

Regards,
Niels