Change Tax condition record

Hi all

I want to change the condition record for excise duty, for that we use JMOP,

when i go for FV12, i am able to change the validity period.

I have changed the validity period by 25.02.2009 to 31.03.9999 and excise duty by 8%

and validity period 08.12.2008 to 24.02.2009 and excise duty by 10%

but when i make the PO, system is picking same excise for both period.

Please help.

Thanks & Regards

Pankaj Garg