Any way to commit User/User Group import with Command Line Import Wizard?

HI,    I've followed the instruction on the businessobjects administration guide to import BOE objects with command line. My environment is BOE XI 3.1.    I can import the reports/links of the biar into the destination BOE, however, users/user group importing always failed. No matter how I tried, the command line still returned the error code:  "...Commited attribute list 'SI_ADM_ADD_USERS_TO_USERGROUP,  SI_ADM_ADD_USERS_TO_USERGROUP'  include non-existed objects..."    Anyone comfronted the same problem before? Any suggestion is appreaciated. Best Regards, Vincent Li