now i got what i done wrong
the path was the problem
if i write it in this way
str_cpy(some_empty_string, save_dir);
it does not work, couz the save_dir contains not the full path
if i declare save_dir like this ( like the manual describes )
str_cpy(save_dir,"game_scores");
save_dir contains only game_scores but not the full path
i saw it when i write this to a textfile
file_str_write(save,save_dir);
so, everytime when i copy this entity it was copied into oblivion
now i use this solution
STRING* path_str = str_create(_chr("\\models\\"));
STRING* target_name = str_create(_chr(work_dir));
str_cat(target_name,path_str);
str_cat(target_name,filename);
file_cpy(target_name, filename);
but thanks for all your help