N=2 and N=3 Heisenberg chains are to simple for spinpack, because spinpack uses symmetries and so matrix size becomes to one. Use minimum N=5 sites or switch off all symmetries to see the full base:
config.h: #define CONFIG_NOS1SYM 1 #define Sud 0 daten.i: verbose=33 x3 99 sym_k= -9999 nud=1,1 # ud-subspace a0 nud=0,2 # dd-subspace a0 nud=2,0 # uu-subspace (same as dd-subspace) a0