I've been able to insert images and bar codes into fields in my database without issue. When I consider ways that this script step might fail, what I can think of is that any of the "insert" scripts steps do not work unless the target field is present on the current layout and browse mode access is permitted. If the field is not present on the layout or browse mode access is not allowed, any script step starting with "insert" will fail to work.
Insert steps also trip some script triggers that you might set on the field, so that is also a detail to consider.
Thanks Phil! It was that I didn't have the field on the layout. I was trying to pass it a container that I didn't necessarily need to have displayed. So when I put the field in the layout, it works.