Error in mass updating table

Hi All ,

i have a requirement where i need to update the IT0040 for subtypes 91, 93, 94.

I am doing a direct table update which we want to follow first i am locking the pernr then updating the IT0040-LOBNR field and then unlocking the pernr. The program updates fine if we run for some pernrs but when we ran it for all pernrs in database some pernrs got updated and for some got the ERROR MESSAGE as Personnel Numbers couldn't be locked . I am using the FM BAPI_EMPLOYEE_ENQUEUE for locking and BAPI_EMPLOYEE_DEQUEUE for unlocking pernr . Anybody can you please tell me why i am getting the message as Personnel numbers coudn't be locked . Is it the problem with the FM call.

Thanks,

Latha.