I've decided to restore to an old save and play it through fast to that point, to see if I did something that might have tripped the door. One thing I can think of is that I went into the bar *before* I was invited. The posion immunity implant made it easy to clean out the chemicals in the dispensers. After I left, I found that I couldn't go back inside...
Perhaps it's a glitch with the game?
Regardless, I will be to that point in the level soon and will let you know if it works!
-m