Manage Display Tab Won't Load - 500 Error

I've worked with Field Group and Display Suite together for quite a while now, and never run into this problem before. The only difference between then and now is that the current project involves many more fields than previous projects have.

While setting up a content type, I was able to add all my fields, and set the Display up using Field Groups, with Display Suite set to None. Then I applied a Display Suite format (fluid two column stacked), and everything broke. I can no longer get the Manage Display page to load for this content type, though Manage Fields loads just fine. When Field Groups is on, the front-end page doesn't load any fields that were inside groups.

This only applies to the content type I was working on. It has about 12 custom fields, and 7 groups. If I turn off Field Groups module the Manage Display page loads as normal, whether Display Suite is on or not, so I'm fairly sure this is a Field Groups issue.

Thanks