Diagnosis
The blender's lid interlock safety system is not registering the lid as fully secured. The flashing 'lid' message is the specific alert for this.
How to Fix It
First, ensure the lid is correctly aligned with the arrow on the jar pointing toward the blender base's front. Press down firmly on the center of the lid until you hear a distinct click. The flashing 'lid' message should disappear.
If That Didn't Work
Inspect the three plastic tabs on the underside of the jar lid. If one is cracked or broken, the magnetic sensor in the base will not engage. A damaged lid requires replacement.
Heads Up
Do not attempt to bypass this safety by holding the lid down manually. The motor will not engage without the correct magnetic signal from an intact lid.