Importing Old Studio Courses

My boss and I recently realized that some of the courses we (or contractors) created in Studio don't function properly for a *very few* users, typically in conjunction with Windows 8 for some reason. What we found is that Studio courses wouldn't work properly, but Storyline courses do. For this reason, we decided to convert old courses from Studio format to Storyline format. Should be an easy solution since I've done this before, right?

Here's where the trouble comes. I'm trying to import two courses created by contractors, but when they get *thisclose* to finishing the import, they stall out. I can let them sit for half an hour and they won't finish importing. I then tried importing one slide from one course and it *still* stalled out. The really weird thing is that when it started stalling out (not when I started the import) the import window said it was trying to import an Engage interaction, and the slide I was importing was not an Engage interaction. It was just a regular PowerPoint slide with audio.

The strangest thing, though, is that I'm only having this problem with the two courses created by the contractors. I have a full zipped package (which I extracted all files from before trying to import) that includes all quizzes and interactions in one folder. Does anyone have any idea why those courses might be getting stuck during import? Any advice is appreciated!