Model Reference Neural Control

If anyone can help I would really appreciate

.Im trying to train a Neural Network in order to control the damping coefficient in a half car suspension system.

The control signal varies the damping coefficient trying to have the performance of the reference system. This is the model reference performance vs the road profile. As you can see the suspension system its working.

I'm using a random reference to simulate the road profile. but when I try to train the NN I got the following error.

Any idea how to solve it? Thanks in Advance