A required resource...

Hi all.

I have a dialog based app that appears as a bunch of slides that
the user can cycle through. Basically, all I'm using on each slide
is DrawText() and LineTo() to draw text and some simple lines. I switch
between a few fonts and a few pens.
Everything looked fine until I stumbled across this problem:
if I erratically start hitting my "next" and "previous" buttons
(not fast-- just certain combinations like, for example, "next",
"next", "previous","next" and then 3 "previous"), the screen
freezes up and I get what looks like
half of a dialog box that says "A required resource"-- that's all
that it says.

Someone suggested to me that maybe I wasn't freeing up pens and things when
I was done with them, but I've checked that carefully. Can anyone suggest
something else that I might look for?

Thanks so much.

-Haven