I have cleaned my machine and put the grinder back inside its housing but it says the grinder is blocked and won't operate. I cannot understand where it can be blocked.

You removed the grinder? Or you removed the outer burr from the grinder? It can be tricky to get back in place with the correct lineup. If you don't do it just right, it won't sit down in place like it is supposed to. Here are the full instructions, you may just need the last little bit about lining the burr up on reassembly.

From wholelattelove website:
You do not need to clean the grinder as often as you may think. Usually we do not recommend cleaning the grinder unless there is a problem with calibration or a clog. Avoiding oily beans, flavored beans, and beans stored in the fridge or freezer will typically prevent issues.

If you do experience issues with your grinder, cleaning it is the most common solution. To clean your grinder, follow these directions:

1. Remove the water reservoir, turn off and unplug the machine.
2. Take the cover off of the bean hopper and vacuum out the beans.
3. Remove the 3 Phillips head screws that are in the bean hopper.
4. Lift up the bean hopper and set it aside.
5. Open the machine's service door and remove the drip tray and the brew group.
6. Remove the rubber gasket from the top of the grinder area.
7. The grinder is made up of 2 pieces. The inner piece has 4 tabs that the rubber gasket sits on. The outer piece has teeth in a ring on the exterior covering ½ the circumference.
8. Rotate the outer ring 180 degrees counterclockwise. You should be able to lift off the inner ring. There is a red spot on the outer collar which should now be facing the 9 0'clock position when you are at the front of the machine.
9. Vacuum out all of the beans and ground coffee.
10. If possible, use a small pipe cleaner to get grounds out of the "pathway" going to the front of the machine. It is located on the floor of the grinder at about the 5 0'clock position.
11. Above where the brew group would be located, there is a gray triangular tab attached to a door on a hinge. Pull down on the triangle - coffee grounds may come out.
12. Look above the trap door and you will see the other end of the chute. Vacuum out the chute and clean with a pipe cleaner.

Reinstalling

1. Drop the inner burr onto the grinder with the tab that has the red and blue marks facing the right hand side of the machine at approximately the three-o'clock position.
2. Rotate the outer collar so that the red mark lines up the red/blue marks on the inner burr.
3. Reinstall the rubber gasket that goes over the grinder. The slots in the gasket line up with the four tabs of the outer burr.
4. There is a straight piece located directly to the right of the grinder. This is your dosage control. There is a piece that can slide backwards and forwards on this dosage arm. Push this arm all the way to the back of the machine.
5. Set the knobs in the bean hopper to #0 on the grind setting knob. Set the doser knob all the way to the plus setting. Now place the hopper back into the machine.
Note: You may have to rotate one or both of the knobs, a small amount, to get the bean hopper to set down on its supports.
6. Install the 3 screws.
7. Replace the water reservoir.
8. Fill the bean hopper with a cup of beans.
9. Plug in and turn on the machine.
10. Reinstall the brew group and the drip tray.
11. Once the machine warms up, press the small coffee button. When the grinder comes on set the grind setting to 6.
Note: You may have to press the small coffee button twice or 3 times before the machine will make a cup of espresso.