I downloaded aerial images from National Map to use as photo scenery. Tried using gdalwarp to convert images to wgs84 projection. Data provided was NAD 83 / UTM zone 16. Spatial Reference.org returns this as EPSG:26916(changed from 16916 to 26916). I get "ERROR 6: EPSG PCS/GCS code 26916 not found in EPSG support files." when I tried to convert the first image. Does anyone know what causes this?