accounting Doc not generated at the time of debit note cancellation doc released vf02,vfx3

Hi,

my client has created debit note then accounting Document generated. after this my client cancelled this debit note.

when he was released debit note cancellation doc to accounting then accounting document was not generated.

Error is:

Accounting Determination missed for account type s in line item 1026.

Now my questions are:

1. when we created debit note then accounting document was generated  so here no account assignment problem.

when we released debit note cancellation doc to accounting then accounting document was not generated. so here accounting determination problem why came ?

2. In debit note 150 line item is there. but in error msg system shows 

Accounting Determination missed for account type s in line item 1026.

why 1026 came ?

Thanks&Regards,

shaik Jani