This looks exceptionally good, I've only played around for a minute or so and as is usual for me, have found some minor niggles.
The exit button either shouldn't be on the toolbar at all, or at the very least, not right below the file menu, it's very easy to click it by accident.
The icons are a little awkward to figure out, they might benefit from being a little larger and maybe give them some colour or at least shading.
Got a repeatable access violation: If you start the program, create an object, click exit, but then cancel and retry exit.
The exit button either shouldn't be on the toolbar at all, or at the very least, not right below the file menu, it's very easy to click it by accident.
The icons are a little awkward to figure out, they might benefit from being a little larger and maybe give them some colour or at least shading.
Got a repeatable access violation: If you start the program, create an object, click exit, but then cancel and retry exit.