Hi Sugan,
Are u checking the availability in released production order or created production order. Please confirm. In OPJJ (PP ATP Check) you have mentioned that "Include Dep.Reservations = Only withdrawable reservations (A)" ie; you are considering only Released Production Order reservations only.
Refer the SAP Help.
SAP Library - Production Orders (PP-SFC)
Thanks & Regards,
Ramagiri