How to get to the Chemical Plant in the quest Invisible Threat

Follow the marker, but do not approach the chemical plant from the east. Instead, go to the left side of the entrance.

You should eventually approach the building from the southwest corner. The guards will be busy shooting dogs or someone else, and another soldier who stops you will immediately recognize the main character as Skif and allow you to enter the Chemical Plant.

This is a simple way to bypass the error associated with the guard at the far entrance.