This appears to be because pandatool/src/lwo/iffInputFile.cxx always returns false:
bool IffInputFile::
open_read(Filename filename) {
filename.set_binary();
VirtualFileSystem *vfs = VirtualFileSystem::get_global_ptr();
istream *in = vfs->open_read_file(filename, true);
if (in == (istream *)NULL) {
return false;
}
set_input(in, true);
set_filename(filename);
return false;
}
Changing the last false to true allows the converter to proceed.