I have completed the Coldwater mission and all other mission up to that point. When I return to Bunker Delta, the turn indicator combat screen is present in the lower right hand corner, but there is no yellow bar. I cannot select any of my characters in order to give orders. I can only select the menu, PIP, map, etc. buttons. Its as if I'm in turn-based combat against an opponent whose turn takes an infinite amount of time. I cannot play beyond this point because I can't interact with any characters to get any more missions. If I go to places other than bunker Delta after the Coldwater mission, (i.e., bunker Gamma, random encounters, other mission sites) everything works well.
I am playing on a Wondows 7 64 bit computer, but the problem also occured (same save game files) on a PC with XP. Reinstalling the game did not solve this, including with a fresh download.
Any help would be appreciated.

Do you have the combat mode set to real time or turn based? If its on turn based try setting it to real time before you got there. That way if it is an enemy you will still beable to move, go kill it and then change it back to turn based after.

The game was in turn based. However, setting it to real-time did not fix the problem. There is no enemy to fight.

Hmm not sure then, do you have any earlier saves you could go back to and see if those are bugged?

There are, but they are several hours of game play ago. From reading posts in other forums, this is a known bug which occurs if combat is initiated in a bunker by accidentally running over somebody or clipping an obstacle with a vehicle on the way to the exit grid. That bunker then becomes unplayable. The solutions, as I undestand it, would be:
1) Start over (no way, I've already dropped about 50 hours on this game).
2) Restore to a point before the bunker became corrupted (don't have any).
3) Forget about the game and move on (tempting right now).
4) Obtain saved game files from a point where that bunker is no longer necessary (bunker epsilon missions in my case) and play with someone else's characters but at least be able to finish the game).