Excise Error at Miro

Dear All,

I have created a Service tax code (VAT-5% on(70% B. value)+Serv.Tax 12.36%on(30%)) copying from another tax code to be used in a PO for material that doesn't attracts excise. The PO is basically created for subcontracting. Now the problem is post MIGO when i do a MIRO i get an error that "Excise Invoice Not Captured" what is the possible reason ? When we take a different tax code it works smoothly.

best regds

Subha