Look here for an explanation of the codes

Er 01 - Debris is trapped in the edge cleaning brush. Inspect and clean it

Er 02 - Debris is trapped or tangled around the agitators. Inspect and clean them

Er 04  - Left drive wheel has become overloaded. Check that debris has not been tangled around it.

Er 05 - Right  drive wheel has become overloaded. Check that debris has not been tangled around it.

Er 07 - One or both of the drive wheels is not making contact with the floor. Check and clean them

Er 08 - Bumper problem. Check it is not damaged and moves freely

Er 09 - The dust container is not fitted or has not been fitted in properly. Fit the dust box by pushing it home until it locks in place

below is example of Error code 01