Cannot create a record in Number sequence references (NumberSequenceReference). Datatype number sequence properties: 450, CEM .None. The record already exists.

HI

when i try to create a number sequence for PO,

following error - I set the scope to Company and added a segment with alpha '###"  

start 1; 999; next: 1

When I try to add reference -: Purchase ->Purchase order, Above  error is reported:  

"Cannot create a record in Number sequence references (NumberSequenceReference). Datatype number sequence properties: 450, CEM      None.

The record already exists."