Bread-Bakers v006.n074.5

I bought some Red Star yeast at the store because that was all they had.  
I have made 4 loaves of bread with it and they have all risen badly.
I just called Red Star and did the test they gave me and it turned out 
perfect.  It was 1/2 cup very warm water, 1 teaspoon sugar and 2 1/4 
teaspoons (1 packet) yeast.  Let it sit for 10 minutes.  If it rises to 
the 1 cup mark, the yeast is fine.

Any ideas why this jar of yeast won't rise my bread when it passes the test?

I used the last jar I had ( the brand with the yellow label) with this 
bag of flour and it worked just like it should.

Kelly