To debug this, add --no-submit-stales. If rejects drop off to near zero, then the cause is network connectivity and you should look for a better pool or try to improve your Internet connection. If they don't, then these are invalid shares, so you should back off on the engine clock and/or intensity settings.

(OTOH If your rejects are at 100% then you're just making some sort of very basic error that you should be able to figure out on your own.)