Error 26 on a Roomba means ***the vacuum is experiencing insufficient airflow***. Here are some things you can try:
* Clean or replace the bin filter
* Remove the bin
* Inspect the vacuum port
* Remove any foreign debris
* Press and hold the clean button for 20 seconds
* Wait 60 seconds
* Press the clean button once
You can also try opening the motor assembly and clearing dust.
Can you share your exact model number? The model number is printed near the left wheel, on the underside of the robot.