It sounds as though your machine hasn't fully registered the descale that you carried out.
Please try the following steps in order and see if it resolves the issue.
Empty the water tank will all but 1.5 inches approximately of water.
Hold the steam button for 10 seconds until all 3 lights flash in sequence.
Turn the steam dial to the on position, remembering to place a container under the steam arm.
Press the steam button to start the descaling process with the water.
Once you run out of water and the descale process stops you will find the light still flashes, whilst this is flashing put another 1.5 inches of water into the water tank, empty the container under the steam arm and press the steam button again for the machine to start rinsing.
Once you have run out of water again, turn the steam dial back to the off position. This should register the descale for you, therefore turning out your flashing light.