Document Numbering

Hi All

I am trying to create a different numbering series in outgoing payment.In the primary series the first num and next num is 1.In the new series (CD) i am giving 1 for both first and next number and in period indicator i am selecting default and when i am updating it there is an error which reads:"series primary overlaps object outgoing payments". and when i am changing the period indicator to another option than also its not working.

need suggestion

rgs

anand