bjkg, what he’s saying is that his drive cannot read dual/double-layer media, not that he burned one and cannot read it. I’m guessing it has to be a problem with your hardware jomtones - probably a fault with detecting DL media. Is this drive old? Cleaning the lens might help, although it’s also possible there might be a bug with the firmware that your drive has right now that causes this. I’m not sure if there were drives made that could not read DL media but if the problem persists it could be one of the two that I’ve mentioned before - but certainly hardware-related (unless you have virtual drives installed in your system, which are also known to screw with physical drives’ capabilities).
You might try using an external drive (if you have one) to read the DL DVD on that specific laptop and see if the problem’s software-related. Otherwise, you might have to wait a bit for other members’ input as I’m all out of things to say.