Hi, this error is usually caused by the bump sensor getting jammed by debris (such as grass clippings). The software checks that the bump sensor is not activated when the robot starts. If it is activated, it stops with the error so you can have the opportunity to correct the problem.
The solution is easy, just remove the outer cover, inspect the bump sensor arms where the recharge bolts screw on. Jiggle them and make sure you hear the internal micro-switch clicking. When you re-assemble the cover, check that the foam pads are present under the bump sensor arms and make sure the white grommet slides into the metal slot on the clear cover. Then confirm the problem has disappeared. If the error comes back, it could mean the micro switch failed and you need to replace it. Generally we have the part in stock. Or, you can wire out the objects by laying new perimeter wire, if it your wire is not over 1500 feet already.
RobotLady