Hi Eugene,
I've fixed the bug in DSSR's .cif parser, and updated the software to 
v1.3.4-2015sep06 on the download page. Please have a try and report back how it goes.
The originally DSSR .cif parser should have worked, since it did not expect a specific order of the .cif 
_atom_site fields. As it turned out, however, a negligence assumed ATOM/HETATM (
_atom_site.group_PDB) to be the first field, instead of its actual position index in the .cif file. In this context (for RCSB PDB entry 
5aj0), it is also interesting to note that the 
x-, 
y-, 
z-coordinates are now represented in the order of 
z, x, and y (colored 
red below). 
loop_
_atom_site.type_symbol 
_atom_site.pdbx_PDB_ins_code 
_atom_site.label_seq_id 
_atom_site.occupancy_esd 
_atom_site.B_iso_or_equiv_esd 
_atom_site.B_iso_or_equiv 
_atom_site.auth_asym_id 
_atom_site.label_asym_id 
_atom_site.pdbx_formal_charge 
_atom_site.label_entity_id 
_atom_site.auth_seq_id 
_atom_site.occupancy 
_atom_site.id 
_atom_site.pdbx_PDB_model_num 
_atom_site.group_PDB 
_atom_site.label_atom_id 
_atom_site.label_comp_id 
_atom_site.Cartn_y_esd 
_atom_site.label_alt_id 
_atom_site.Cartn_z_esd 
_atom_site.auth_atom_id 
_atom_site.auth_comp_id 
_atom_site.Cartn_z
_atom_site.Cartn_x 
_atom_site.Cartn_y  
_atom_site.Cartn_x_esd 
P  ? 1    ? ? 20.00  A3 A  ? 1  1    1.00 1      1 ATOM   P     C   ? . ? P     C   -54.864  60.295   10.209   ? 
O  ? 1    ? ? 20.00  A3 A  ? 1  1    1.00 2      1 ATOM   OP1   C   ? . ? OP1   C   -53.786  61.291   9.998    ? 
For the record, here is the output of running the updated command: 
x3dna-dssr -i=5aj0.cif -o=5aj0.out:
[i] '5aj0.cif' taken as in .cif format by file extension.
Processing file '5aj0.cif' [5aj0]
total number of base pairs: 2621
total number of multiplets: 309
total number of helices: 175
total number of stems: 347
total number of isolated WC/wobble pairs: 160
total number of atom-base capping interactions: 328
total number of hairpin loops: 118
total number of bulges: 80
total number of internal loops: 194
total number of junctions: 67
total number of non-loop single-stranded segments: 65
total number of kissing loops: 7
total number of A-minor (type I and II) motifs: 82
total number of ribose zippers: 46 (380)
total number of kink turns: 5
[w]  cross-paired segments in separate chains, be *careful* with .dbn
Time used: 00:00:07:35Once again, thanks for reporting the bug -- it's users like you that help improving DSSR!
Xiang-Jun