i just did it today. if you go to the main disney site and click on "my disney experience" and then on the right hand side it will say online check-in is available. if you try to click online check in from the dvcmember site and you are logged onto the main site, it will not work properly.
or you can go to mydisneyreservation.com and check-in. make sure you are logged out of disney main site and dvcmember. you will need your reservation number.