Hi,
Just a thought... sounds like you might have mis-typed the object's model filename in your CONFIG.CPP file. Check the "MODEL = " line and make sure that it's correctly pointing to a .P3D file and not a .PBO file.
I've inadvertantly made that mistake a couple times myself, automatically typing .PBO instead of .P3D... Nowdays I avoid that problem altogether by leaving off the .P3D extension in the filename string.