If you are talking about Zulag 2, in Rupture Farms (the first time you visit it) you aren't aloud in, simple as that, you must wait until the end of the game when you revisit Rupture Farms to gain access to it. This is the same with the electric wall that you cant get through, when you go down the elevator and walk right 1 screen.
I hope i have answered the question correctly, i got a bit confused with your wording, but hopefully i nailed the correct answer
