I haven't been able to submit a special meal request on eligible itineraries for a few weeks. The error is
System Unavailable
We're sorry but this service is not available at this time. Please try again later.
If you need assistance, call Delta at 800-323-2323, or at the number on the back of your SkyMiles membership card. For non-U.S. based customers, please call the Delta Reservation Sales office for your country.
SMS can process it without a problem.