I think it should be
LOADPNG(device_befs, iDeviceGeneric);
LOADPNG(device_befs_o, iDeviceBEFS);
instead of
LOADPNG(device_befs, iDeviceBEFS);
LOADPNG(device_befs_o, iDeviceBEFS_o);
or GUI won't start if there's no device_befs.png in theme folder.
Second argument for LOADPNG is alt_img (alternative image I guess)
#define LOADPNG(img, alt_img) if (loadThemeImage(#img, alt_img) != 0) { return 1; }