An important difference between ordering from BatchPCB and ordering from OSH Park is the need for a board outline gerber.
Since boards can be any shape and can have cutouts and slots, there needs to be a gerber file that tells the fab this information. We use a board outline gerber for this.
The Quick Fix
BatchPCB wanted the board outline on another layer, like top silkscreen, or top copper. The quickest path to converting your gerbers for use at OSHPark is to simply make a copy of the file that has your board outline in it, and give it a “.GKO” extension.
If you’re using Eagle CAD, consider just uploading your .brd file. As long as your outline is drawn on the Dimension layer, the website will make all the gerbers it needs.
In KiCAD, the board outline is the PCB Edges gbr. OSHPark understands the KiCAD naming scheme natively.