Form buttons invisible

Question

I've design a windows form with VS2005 C#.  I have two buttons along the bottom of the form, which show up just fine in the designer.  When I run the application on my computer, it looks great.  However, when I run it on a friends computer, the buttons don't show up properly.  Instead of a button with text, I just get the background form color with the top and left lines of the button border.  If I click on the area where the button should be, I get an event, so it seems that I have some kind of problem making the button visible.  The button properties are visible = true and enabled = true, so I just can't figure out what is wrong.  All other controls, like tickboxes, look ok.

Any clues about this one?

Thanks
Simon