Customer contact creation in R12.1.1--> 'Invalid value for subject_id. Please enter person id value

Hi, we are on R12.1.1 and set up the profile options HZ:Generate Party Number/Generate Party Site Number/Generate Contact Number values to 'No' so the user can manually enter these values. We were able to acheive this. But when we are trying to create the customer contact, there are 2 fields Registry Id(party number in HZ_PARTIES table) and Site number which are mandatory. When i am trying to give some value in the Registry Id field(not the customer party_number), it is throwing me an error 'Value for Party number must be unique', if i change it to something else 2nd time it