Sougata,
I used FM FKK_O_LOCK_METHOD_SAVE to insert a new record in DFKKLOCKS table. Since i am changing one of the key fields(TDATE), always it inserted a new record rather than updating existing record. So if insert was successful, I deleted the existing record using FKK_S_LOCK_DELETE.
Thanks a lot everyone for all your valuable inputs.
Aspire