Q: can't burn dvd after latest update

Running 10.11.4 on Imac I5, late 2013 with Sony external dvd drive. Always had trouble getting it to start burning but now can't burn dvd at all. Get connection errors, weak connection errors and even multiple dvd icons on desktop. Using toast 14 with good quality dvd. Usb connected to directly to mac. ResetPRAM, moved usb to different ports. Sometimes dvd will mount but not be available or when ready to burn get error messages. Before last update worked most of time. Such a simple tsk, thats always been an ordeal since drive removed.