marco_c:
Are you sure that you are mapping the DP (decimal point) output signal from the IC to the right column or row?
I think Marco nailed it there.
Look at the sequence the above page from the data sheet: left-to-right it's DP, A, B, C, D, E, F, G
Not: A, B, C, D, E, F, G, DP, as I think you numbered them.
row led pin chip pin
1 9 14 SEG A
2 14 16 SEG B
3 8 20 SEGC
4 12 23 SEG D
5 1 21 SEG E
6 7 15 SEG F
7 2 17 SEG G
8 5 22 SEG DP