Hmmmmm.......
Is it common for Tiger Barbs to just up and die? No, I dont think so; they are know to be hardy fish. How long do you have them? If they are new, it could simply be stress from the move. Edit; It jsut copped that you said you had him a week. Hmmmm, could be stress, I guess. Most likey not though, as too much time has passed.
How many were in the shoal? If it were too small, say 2-4 it may have been picked on to the point of death. Same goes for what tank mates you have.
Are you over feeding? This could be an issue. With Tigers, look to see if they are swiming with their heads dowm, if so they are prob overfed. Are you giving them any greens? Tigers like a small bit of green in their diet, cucumber, for example. I dont think a lack of greens would have killed it, but that is a nice, and little know, tip for the ones you still have.
Prob no harm knowing what size your tank is.....