"Unable to create Window" Question

I know there has to be a simple answer to this one.

Is there any way (for debugging purposes) to track the consumption of
windows/window resources consumed as forms are created?

I have a situation where I have an SDI app, with a graphic on the main
screen.  From there a form is created and shown modally.  That form in
turn creates another which is also shown modally.  This third form then
creates a fourth form, but when it attempts to display it modally, it
generates an "Unable to create Window" error. I am assuming that this
message relates to being out of GDI or some other resource, but w/o
knowing when and how these resources are being consumed, it is difficult
to debug.

Thanx in advance for any help.
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