Customer Additional Information form error

hi,

Customer with null site already exists. When defining the customer  with site on customer additional information , getting the following error:

APP-FND-01206: This record already exists. You entered a duplicate value or sequence of values that must be unique for every record.

Checked if there was record with site. There is no record for the same customer with site. But still getting this error.

This is happening for all records of customers.

please let me know how to resolve this.

Thanks

Yogesh