Archiving of Cost centers (Cost center master not archived because transaction data exists)

Hi Experts,

We are implementing the archiving cost center master data using CO_CCMAST archiving object.. here we are getting the message like

Cost center master not archived because transaction data exists even after archiving the CO_ITEM...

Could you please help me on the above  for archiving of CO_CCMAST..

Thanks,

Rajesh b