Diagnosis
Accumulated grease and carbon have solidified, acting as an adhesive between the grease tray and the support rails. This is a maintenance issue, not a defect.
How to Fix It
Do not force it. Heat the grill to a medium temperature (approx 300°F) for 10-15 minutes to soften the grease. Turn off the grill and allow it to cool until warm, not hot. Wear gloves. Use a putty knife or a stiff plastic scraper to carefully break the seal between the tray and the side rails. Gently wiggle the tray free. Clean the tray and the rails thoroughly with a degreaser.
If That Didn't Work
For severe cases, remove the tray for a deep clean. After warming the grill and scraping, you may need to lift the front of the tray upward slightly to disengage it from the rear support before sliding it forward.
Heads Up
Clean the grease tray and drip pan regularly to prevent grease fires. A full tray is the primary cause of flare-ups in this model.