How do I continue playing?

You have to do this level on the first try. When you start the mission take a few steps out and then manually save. Then go to the Water Tower and snipe all those guys. When you go back down to the door to answer the door, don't go in. Manually save your game again and when it's done PULL OUT YOUR MEMORY CARD then unpause your game. There should be dozens of guys in the room this time. If you get killed or fail the mission then put your memory card back in and load it again from there on you should bypass this glitch. In short:

1. Playstation is turned off
2. With game disc and memory card in place, turn on Playstation
3. Load the game (it should be at 4:28). If its not, more about that later
4. The cutscene with Jack and Tony begins
5. Remove the memory card
6. The following message will appear: "Warning, memory card removed . . . Use save game option to manually save progress & re-enable autosave?"
7. Press X for 'OK'
8. Re-insert memory card
9. Watch the cut scene
10. "Previously on 24" dialog box appears. Press X
11. Play the game as usual. If done properly, many men will enter the building during gameplay
12. Save when you have completed the mission.

If your memory card is at 4:41 . . .
Go to 'restart mission' and do a save during the cutscene. You will overwrite 4:41, and be back at 4:28

Credit goes to http://cheats.ign.com/articles/698/698323p1.html