What could be causing it ?
If a dishwasher replacement didn't fix it, then you didn't do a complete job nor follow instructions. Supply and Drain lines should always be replaced with any new dishwasher. This, removes the oops-factor from simply having a clogged Drain line or not reading to remove a new garbage disposal's knock-out plug.
If all of that was done and the above doesn't apply to you, then make sure there isn't packaging material (clear plastic) blocking the draining. Or, call the manufacturer, whom may have hung you out to dry with the China-factor. Appliances are hit or miss today and more tend to be a miss immediately or very quickly for a very large percentage.