VB2005 MDI problem

Question

I'm a newbie at VB 2005 and I'm writing my first application. It's an MDI form which opens a 2nd form from a menu. The second form uses a control array to put a grid of buttons on the form. This all works fine. However, when I handle a click event on one of the buttons I want to update a label control on the same form, but the label.text doesn't change! :-(

Originally, I wasn't using an MDI form, just using the form with all the buttons and labels as the mainform, and that worked fine. I assume that the problem has something to do with making this a child of an MDI form, but I can't work it out. I've followed the code in debug and the label.text is being updated fine, but the form isn't being updated. Do I need to do some kind of refresh command to get the form to repaint the controls?

Any help gratefully accepted!