I had this problem before and this was the reply from DeltaAgent:

Quote:
Originally Posted by NOLA Flyer
I too was unable to check-in online last Thursday for a flight from MSY-DFW-LGA. I didn't get an error message, but the box "Proceed to Check-In" was greyed out, as if it were not an option.



Nola Flyer, It looks like you were going to check in thru the My Itineraries page. Log out and go to the Home page

1. Select Online Check-in (in the Flight Tools box)
2. Enter your name and Delta reservation number (e-ticket or credit card also accepted)
3. Select "Go"

You will now be on the Check in page and should have a blue "Check-in Now" button.

This has worked for both Elite and General members who had a grey button under the My Itineraries page.