Sometimes when you have a lot of objects, tiles, or a very large custom map, a generic "An error has occurred" message displays. This error prevents you from adding too many things to the Space that are required to load individually, which can put excess strain on participants' CPU and result in a poor experience for that participant.
If you run into this error, we recommend creating separate Rooms with smaller footprints to divide some of the objects into different Rooms. This will help spread out some of the objects that need to be loaded and allow participants to load them properly.
Another solution that requires more design work is to use a third party software like Tiled to create custom backgrounds with objects built into the background. This will allow objects to load as a part of the background image, instead of individual objects within the Space.