For message VF050 (no accoting doc generated) while billing

Hi All

While billing the exciseble material with CST tax code we are getting the message VF 050 (no accounting doc generate)

When we are releasing the doc form VFX3 we are getting the folloeing message

No account is specified in item 0000001009

Please Help What could be the possible reasons for the same.

Regs

Niti Narayan