OK, finally figured it out and wanted to post maybe to help others...
As you know, there are no doors that really can be entered throughout this game...until this mission! There is a soldier trapped "just outside the warehouse" as the briefing says. But when you get near him, the part where he pops smoke to help you identify his location, you will actually find him in a small house/room, just outside where the smoke is. You need to walk through the door to "rescue" him. I could never find this guy, and just went forward to the other team of soliders waiting further up, and that's where I was stuck because it won't let you do anything - until you rescue that lone soldier first.... Good Luck!
