Error while doing ML81N

HI,

I am facing a serious problem,

I have created a standard service catalog(SSC) and i am using it to do a service purchase order against Cost centre. I have entered all the service data and account assignment in PO level and saved it.

But while doing the service entry sheet and saving it after acceptance. It is shooting arror.

M8 147 :: account assignment RUPA WRX not possible.

can anyone help me out, how to do handle this.

Regards