Thanks for quick reply Mark.
We did not create new account group at customer master and we are creating customers in the same account group. However we had to adjust number range from ( 20000000 to 89999999) to (1 to 89999999). Due to this I had to adjust BP number range also from (20000000 to 89999999) to (1 to 89999999 or ZZZZZZZZ ). Customer creation was fine for new customers which were under 10,000 but business partner is conflicting with existing BPs which were created as contact person.
Since we are not using BP's for contact person in any place, they are of no use sitting as business partner and using the numbers. Hence I am trying to delete existing BPs which were under 10,000 to free up the numbers to re-use for new customers.
Any more suggestions please?