hpf_region_get_target()
uses region_find() and some string manipulation to determine the appropriate path name. Have a look at line 529 and following:
str_clip(str_tmp,3);
str_printf(str_tmp,"path%s",_chr(str_tmp));
if(!path_set(ent,str_tmp)) error("HPF_REGION_GET_TARGET: Path to region does not exist!");
Apparently when you want to use Treg_ and Tpath_ as names you will have to adapt the number in str_clip (change it to 4).
Your enemy/ NPC code looks fine to me. hpf_region_get_target() calls hpf_path_get_target() which calculates corresponding start and target nodes which are then used by a subsequent hpf_path_get() call. You could add a
printf("Start: %d, Target: %d, Max_nodes: %d",(int)start_node,(int)target_node,(int)max_nodes);
before the error() instruction in line 216.
Try disabling hpf_path_get_target_collision (in the *.h file) temporarily, too.
