It looks as if you need a lookup table that outputs the rpm at the queried torque. In that case, torque is monotonically increasing from 0 to 350 Nm, and the rpm is a function of the torque.
Most likely, the table you had created had these values interchanged, i.e. you had tried to output torque at the queried rpm, hence the "monotonically increasing" error.
You can check this by opening the variables that represent the torque and rpm from the Workspace Explorer.
