We've had a one UR5e fail with a C450C4 Error about a missing Force-Torque sensor in the last week. 
Tried to restart the robot with no effect.

We upgraded the robot to 5.11 with no changes. 

All connections have ben cheeked.  

Note:

The robot is equipped with Robotiq 2F-85 & Wrist Camera.

There is no FT 300-S Force Torque Sensor in this robot!!

The robot was turned off for more than 9 months, and the system was fully functional before shutting down it.

Hi @RaiedKassab,

UR e-Series robot models do actually have an embedded Force-Torque sensor in their wrist.

It is possible that an internal connection in the robot has failed during its storage period, making the connection to the FT-sensor impossible.

Historically, it could be solved by replacing the wrist of the robot, but I would highly suggest contacting UR's support so they can advise on the best solution for you.

Hope this helps.

You could also share an picture of the error message. That may help to understand the situation.

Her is the error:

It is an error related to the robot itself. As my colleague suggested, you should contact UR support to get further advice.