So I have a fairly complex PowerPoint I've been working on--it is a complex training program combined with a testing portion that presents multiple choice questions some of which are just text, some of which are graphical, some of which are animated graphics, and some of which are synthesized speech and audio, etc. When the user answers a slide incorrectly, VBA code copies the slide to the end of the presentation so that the user must answer missed questions again to ensure learning the correct response.
Anyway, I had added about 200 slides and then I ran into a problem. After running a certain slide, the VBA code that copied the slide started causing an error of "invalid function" for the simple line of code: oSld.Copy. I then tried manually copying the slide by using CTRL+C in the slide editing window and I got a similar error but worded differently; something like this: "We're sorry, something went wrong that might make PowerPoint unstable. Please save your presentation and restart PowerPoint."
I was completely baffled by this odd behavior and thought perhaps the PowerPoint was balking at the number of slides, so, I reduced the number of slides to only 15 or so, but, the same slide still caused problems at oSld.Copy and CTRL+C.