Error in account coding allocation - ML81n

Dear All,

I am going to create entry sheet from PO service.

1st. Open tcode ML81n and choose PO and item.

2nd. click create entry sheet

3rd. input no reference

4th. click button service selection

5th. after that it will be appear error message ' Error In Account Coding Allocation '

What should i do, please advice...

Cheers,

Nies