Hold on, If you don't reognize it, it is most likley something you added inadvertly. While in object mode, Delete, and it is gone.
It looks like it might be an image, showing up.
If you put all the parts you want to Map, in a folder named (MAP PARTS). Check the list.
When you go to Map, first lock all parts. Then open the MAP PARTS folder, Combine those parts. Next select one Face on the first part you want to Map. Then hold the F key down, which selects all the Faces on that part, then click the uvw tool.