The Citadel Light Freighter is Silhouette 4 and mounts a Medium Tractor Beam. That weapon can only be mounted on Silhouette 5+.
Changing it to a Light Tractor Beam with Range [Close] and Tractor 2 fixes the issue.
Can you please provide the page references for both the freighter, and the text where it states that tractor beams can only be mounted on ships of Silhouette 5?
The Citadel Light Freighter is found on page 261. The table that describes what Size (Silouette) of ship is able to mount which weapons is found on page 271.