Today I was playing close 1-on-1 with a guy and couldn’t use my inhibitor on him - no target error even though he was close and I had full energy bar.
Are you sure that non of your allies already used this module on the enemy?
I am having issues with this module as well,
I have received 1/5 for my contract (so i guess it works) but cannot seem to get another one although i am 100% sure it should of worked a few times.
More information on the modules would be great (hence me being here)
e.g. I presume t toggles but to honest without it working i am now not so sure ?? 
the description is confusing on this one.
does it mean:
1: Target takes less dmg when mod is used on them
2: Target gives less dmg on you when module is on them
The way it reads, it sounds like I supposed to put this mod on my ally to take less dmg from other targets.