From what I understand you're doing the Control Design Onramp in Simulink, specifically, Part 3.2, Linearizing the Plant, Task 3. I am trying to recreate the issue
The instructions state to drag the LTI System mylinsys from the Linear Analysis workspace to the MATLAB Workspace. Your Data Browser should end up looking like this after renaming and dragging:
(you may have to scroll down the MATLAB workspace)
Is this the step where you are facing the issue?
If you are facing problems in the previous step, it may be that you've selected the wrong signal to get the Output Measurement.
However, when in doubt in any step, you can click on the "See Solution" or "Hint" link under the Task to get more information.